Enforce non-null value from getBean and at injection points

Bean-derived null values may still get passed into bean properties and injection points but only if those are declared as non-required. Note that getBean will never return null; a manual bean.equals(null) / "null".equals(bean.toString()) check identifies expected null values now.  This will only ever happen with custom FactoryBeans or factory methods returning null - and since all common cases are handled by autowiring or bean property values in bean definitions, there should be no need to ever manually check for such a null value received from getBean.

Issue: SPR-15829

spring-beans/src/main/java/org/springframework/beans/factory/ObjectFactory.java

@@ -45,7 +45,6 @@ public interface ObjectFactory<T> {
 	 * @return the resulting instance
 	 * @throws BeansException in case of creation errors
 	 */
-	@Nullable
 	T getObject() throws BeansException;
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/ObjectProvider.java

@@ -40,7 +40,6 @@ public interface ObjectProvider<T> extends ObjectFactory<T> {
 	 * @throws BeansException in case of creation errors
 	 * @see #getObject()
 	 */
-	@Nullable
 	T getObject(Object... args) throws BeansException;
 
 	/**

spring-beans/src/main/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.java

@@ -725,7 +725,7 @@ public class AutowiredAnnotationBeanPostProcessor extends InstantiationAwareBean
 
 		@Override
 		public Object resolveShortcut(BeanFactory beanFactory) {
-			return resolveCandidate(this.shortcut, this.requiredType, beanFactory);
+			return beanFactory.getBean(this.shortcut, this.requiredType);
 		}
 	}
 

spring-beans/src/main/java/org/springframework/beans/factory/config/AutowireCapableBeanFactory.java

@@ -268,7 +268,6 @@ public interface AutowireCapableBeanFactory extends BeanFactory {
 	 * @return the bean instance to use, either the original or a wrapped one
 	 * @throws BeansException if the initialization failed
 	 */
-	@Nullable
 	Object initializeBean(Object existingBean, String beanName) throws BeansException;
 
 	/**
@@ -281,7 +280,6 @@ public interface AutowireCapableBeanFactory extends BeanFactory {
 	 * @throws BeansException if any post-processing failed
 	 * @see BeanPostProcessor#postProcessBeforeInitialization
 	 */
-	@Nullable
 	Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
 			throws BeansException;
 
@@ -295,7 +293,6 @@ public interface AutowireCapableBeanFactory extends BeanFactory {
 	 * @throws BeansException if any post-processing failed
 	 * @see BeanPostProcessor#postProcessAfterInitialization
 	 */
-	@Nullable
 	Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 			throws BeansException;
 

spring-beans/src/main/java/org/springframework/beans/factory/config/DependencyDescriptor.java

@@ -252,7 +252,7 @@ public class DependencyDescriptor extends InjectionPoint implements Serializable
 	public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
 			throws BeansException {
 
-		return beanFactory.getBean(beanName, requiredType);
+		return beanFactory.getBean(beanName);
 	}
 
 

spring-beans/src/main/java/org/springframework/beans/factory/config/SmartInstantiationAwareBeanPostProcessor.java

@@ -87,7 +87,6 @@ public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationA
 	 * (typically with the passed-in bean instance as default)
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	@Nullable
 	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
 		return bean;
 	}

spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractAutowireCapableBeanFactory.java

@@ -410,37 +410,36 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	}
 
 	@Override
-	@Nullable
 	public Object initializeBean(Object existingBean, String beanName) {
 		return initializeBean(beanName, existingBean, null);
 	}
 
 	@Override
-	@Nullable
 	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
 			throws BeansException {
 
 		Object result = existingBean;
 		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
-			result = beanProcessor.postProcessBeforeInitialization(result, beanName);
-			if (result == null) {
-				return null;
+			Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
+			if (current == null) {
+				return result;
 			}
+			result = current;
 		}
 		return result;
 	}
 
 	@Override
-	@Nullable
 	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 			throws BeansException {
 
 		Object result = existingBean;
 		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
-			result = beanProcessor.postProcessAfterInitialization(result, beanName);
-			if (result == null) {
-				return null;
+			Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
+			if (current == null) {
+				return result;
 			}
+			result = current;
 		}
 		return result;
 	}
@@ -461,7 +460,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @see #doCreateBean
 	 */
 	@Override
-	@Nullable
 	protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
 			throws BeanCreationException {
 
@@ -535,7 +533,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @see #instantiateUsingFactoryMethod
 	 * @see #autowireConstructor
 	 */
-	@Nullable
 	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
 			throws BeanCreationException {
 
@@ -547,23 +544,23 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 		if (instanceWrapper == null) {
 			instanceWrapper = createBeanInstance(beanName, mbd, args);
 		}
-		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
-		Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
-		mbd.resolvedTargetType = beanType;
+		final Object bean = instanceWrapper.getWrappedInstance();
+		Class<?> beanType = instanceWrapper.getWrappedClass();
+		if (beanType != NullBean.class) {
+			mbd.resolvedTargetType = beanType;
+		}
 
-		if (beanType != null) {
-			// Allow post-processors to modify the merged bean definition.
-			synchronized (mbd.postProcessingLock) {
-				if (!mbd.postProcessed) {
-					try {
-						applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
-					}
-					catch (Throwable ex) {
-						throw new BeanCreationException(mbd.getResourceDescription(), beanName,
-								"Post-processing of merged bean definition failed", ex);
-					}
-					mbd.postProcessed = true;
+		// Allow post-processors to modify the merged bean definition.
+		synchronized (mbd.postProcessingLock) {
+			if (!mbd.postProcessed) {
+				try {
+					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
 				}
+				catch (Throwable ex) {
+					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
+							"Post-processing of merged bean definition failed", ex);
+				}
+				mbd.postProcessed = true;
 			}
 		}
 
@@ -583,9 +580,7 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 		Object exposedObject = bean;
 		try {
 			populateBean(beanName, mbd, instanceWrapper);
-			if (exposedObject != null) {
-				exposedObject = initializeBean(beanName, exposedObject, mbd);
-			}
+			exposedObject = initializeBean(beanName, exposedObject, mbd);
 		}
 		catch (Throwable ex) {
 			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
@@ -624,15 +619,13 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 			}
 		}
 
-		if (bean != null) {
-			// Register bean as disposable.
-			try {
-				registerDisposableBeanIfNecessary(beanName, bean, mbd);
-			}
-			catch (BeanDefinitionValidationException ex) {
-				throw new BeanCreationException(
-						mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
-			}
+		// Register bean as disposable.
+		try {
+			registerDisposableBeanIfNecessary(beanName, bean, mbd);
+		}
+		catch (BeanDefinitionValidationException ex) {
+			throw new BeanCreationException(
+					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
 		}
 
 		return exposedObject;
@@ -904,17 +897,13 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @param bean the raw bean instance
 	 * @return the object to expose as bean reference
 	 */
-	@Nullable
-	protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, @Nullable Object bean) {
+	protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
 		Object exposedObject = bean;
-		if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
+		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
 			for (BeanPostProcessor bp : getBeanPostProcessors()) {
 				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
 					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
 					exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
-					if (exposedObject == null) {
-						return null;
-					}
 				}
 			}
 		}
@@ -954,9 +943,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 				instance = resolveBeforeInstantiation(beanName, mbd);
 				if (instance == null) {
 					bw = createBeanInstance(beanName, mbd, null);
-					if (bw == null) {
-						return null;
-					}
 					instance = bw.getWrappedInstance();
 				}
 			}
@@ -995,9 +981,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 			instance = resolveBeforeInstantiation(beanName, mbd);
 			if (instance == null) {
 				BeanWrapper bw = createBeanInstance(beanName, mbd, null);
-				if (bw == null) {
-					return null;
-				}
 				instance = bw.getWrappedInstance();
 			}
 		}
@@ -1097,7 +1080,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @see #autowireConstructor
 	 * @see #instantiateBean
 	 */
-	@Nullable
 	protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
 		// Make sure bean class is actually resolved at this point.
 		Class<?> beanClass = resolveBeanClass(mbd, beanName);
@@ -1184,9 +1166,8 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @see #obtainFromSupplier
 	 */
 	@Override
-	@Nullable
 	protected Object getObjectForBeanInstance(
-			@Nullable Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
+			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
 
 		String currentlyCreatedBean = this.currentlyCreatedBean.get();
 		if (currentlyCreatedBean != null) {
@@ -1262,7 +1243,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @return a BeanWrapper for the new instance
 	 * @see #getBean(String, Object[])
 	 */
-	@Nullable
 	protected BeanWrapper instantiateUsingFactoryMethod(
 			String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
 
@@ -1698,7 +1678,6 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 	 * @see #invokeInitMethods
 	 * @see #applyBeanPostProcessorsAfterInitialization
 	 */
-	@Nullable
 	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
 		if (System.getSecurityManager() != null) {
 			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
@@ -1715,18 +1694,16 @@ public abstract class AbstractAutowireCapableBeanFactory extends AbstractBeanFac
 			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
 		}
 
-		if (wrappedBean != null) {
-			try {
-				invokeInitMethods(beanName, wrappedBean, mbd);
-			}
-			catch (Throwable ex) {
-				throw new BeanCreationException(
-						(mbd != null ? mbd.getResourceDescription() : null),
-						beanName, "Invocation of init method failed", ex);
-			}
-			if (mbd == null || !mbd.isSynthetic()) {
-				wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
-			}
+		try {
+			invokeInitMethods(beanName, wrappedBean, mbd);
+		}
+		catch (Throwable ex) {
+			throw new BeanCreationException(
+					(mbd != null ? mbd.getResourceDescription() : null),
+					beanName, "Invocation of init method failed", ex);
+		}
+		if (mbd == null || !mbd.isSynthetic()) {
+			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 		}
 
 		return wrappedBean;

spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanFactory.java

@@ -380,9 +380,13 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 		// corner cases, in particular in functional configuration and Kotlin scenarios.
 		// A future Spring generation might eventually forbid null values completely
 		// and throw IllegalStateExceptions instead of leniently passing them through.
-		if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
+		if (requiredType != null && !requiredType.isInstance(bean)) {
 			try {
-				return getTypeConverter().convertIfNecessary(bean, requiredType);
+				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
+				if (convertedBean == null) {
+					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
+				}
+				return convertedBean;
 			}
 			catch (TypeMismatchException ex) {
 				if (logger.isDebugEnabled()) {
@@ -421,9 +425,6 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 				return !BeanFactoryUtils.isFactoryDereference(name);
 			}
 		}
-		else if (containsSingleton(beanName)) {
-			return true;
-		}
 
 		// No singleton instance found -> check bean definition.
 		BeanFactory parentBeanFactory = getParentBeanFactory();
@@ -496,7 +497,7 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 
 		// Check manually registered singletons.
 		Object beanInstance = getSingleton(beanName, false);
-		if (beanInstance != null) {
+		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
 			if (beanInstance instanceof FactoryBean) {
 				if (!BeanFactoryUtils.isFactoryDereference(name)) {
 					Class<?> type = getTypeForFactoryBean((FactoryBean<?>) beanInstance);
@@ -605,7 +606,7 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 
 		// Check manually registered singletons.
 		Object beanInstance = getSingleton(beanName, false);
-		if (beanInstance != null) {
+		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
 			if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
 				return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
 			}
@@ -613,10 +614,6 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 				return beanInstance.getClass();
 			}
 		}
-		else if (containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
-			// null instance registered
-			return null;
-		}
 
 		// No singleton instance found -> check bean definition.
 		BeanFactory parentBeanFactory = getParentBeanFactory();
@@ -1014,10 +1011,6 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 		if (beanInstance != null) {
 			return (beanInstance instanceof FactoryBean);
 		}
-		else if (containsSingleton(beanName)) {
-			// null instance registered
-			return false;
-		}
 
 		// No singleton instance found -> check bean definition.
 		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
@@ -1631,13 +1624,8 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	 * @param mbd the merged bean definition
 	 * @return the object to expose for the bean
 	 */
-	@Nullable
 	protected Object getObjectForBeanInstance(
-			@Nullable Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
-
-		if (beanInstance == null) {
-			return null;
-		}
+			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
 
 		// Don't let calling code try to dereference the factory if the bean isn't a factory.
 		if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
@@ -1782,7 +1770,6 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
 	 * @return a new instance of the bean
 	 * @throws BeanCreationException if the bean could not be created
 	 */
-	@Nullable
 	protected abstract Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
 			throws BeanCreationException;
 

spring-beans/src/main/java/org/springframework/beans/factory/support/BeanDefinitionValueResolver.java

@@ -205,6 +205,9 @@ class BeanDefinitionValueResolver {
 						"Error converting typed String value for " + argName, ex);
 			}
 		}
+		else if (value instanceof NullBean) {
+			return null;
+		}
 		else {
 			return evaluate(value);
 		}
@@ -309,12 +312,13 @@ class BeanDefinitionValueResolver {
 			Object innerBean = this.beanFactory.createBean(actualInnerBeanName, mbd, null);
 			if (innerBean instanceof FactoryBean) {
 				boolean synthetic = mbd.isSynthetic();
-				return this.beanFactory.getObjectFromFactoryBean(
+				innerBean = this.beanFactory.getObjectFromFactoryBean(
 						(FactoryBean<?>) innerBean, actualInnerBeanName, !synthetic);
 			}
-			else {
-				return innerBean;
+			if (innerBean instanceof NullBean) {
+				innerBean = null;
 			}
+			return innerBean;
 		}
 		catch (BeansException ex) {
 			throw new BeanCreationException(
@@ -344,8 +348,10 @@ class BeanDefinitionValueResolver {
 	/**
 	 * Resolve a reference to another bean in the factory.
 	 */
+	@Nullable
 	private Object resolveReference(Object argName, RuntimeBeanReference ref) {
 		try {
+			Object bean;
 			String refName = ref.getBeanName();
 			refName = String.valueOf(doEvaluate(refName));
 			if (ref.isToParent()) {
@@ -355,13 +361,16 @@ class BeanDefinitionValueResolver {
 							"Can't resolve reference to bean '" + refName +
 							"' in parent factory: no parent factory available");
 				}
-				return this.beanFactory.getParentBeanFactory().getBean(refName);
+				bean = this.beanFactory.getParentBeanFactory().getBean(refName);
 			}
 			else {
-				Object bean = this.beanFactory.getBean(refName);
+				bean = this.beanFactory.getBean(refName);
 				this.beanFactory.registerDependentBean(refName, this.beanName);
-				return bean;
 			}
+			if (bean instanceof NullBean) {
+				bean = null;
+			}
+			return bean;
 		}
 		catch (BeansException ex) {
 			throw new BeanCreationException(

spring-beans/src/main/java/org/springframework/beans/factory/support/ConstructorResolver.java

@@ -348,7 +348,6 @@ class ConstructorResolver {
 	 * method, or {@code null} if none (-> use constructor argument values from bean definition)
 	 * @return a BeanWrapper for the new instance
 	 */
-	@Nullable
 	public BeanWrapper instantiateUsingFactoryMethod(
 			final String beanName, final RootBeanDefinition mbd, @Nullable final Object[] explicitArgs) {
 
@@ -576,9 +575,6 @@ class ConstructorResolver {
 						mbd, beanName, this.beanFactory, factoryBean, factoryMethodToUse, argsToUse);
 			}
 
-			if (beanInstance == null) {
-				return null;
-			}
 			bw.setBeanInstance(beanInstance);
 			return bw;
 		}

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -1129,14 +1129,27 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 			if (autowiredBeanNames != null) {
 				autowiredBeanNames.add(autowiredBeanName);
 			}
-			return (instanceCandidate instanceof Class ?
-					descriptor.resolveCandidate(autowiredBeanName, type, this) : instanceCandidate);
+			if (instanceCandidate instanceof Class) {
+				instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
+			}
+			Object result = instanceCandidate;
+			if (result instanceof NullBean) {
+				if (isRequired(descriptor)) {
+					raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
+				}
+				result = null;
+			}
+			if (!ClassUtils.isAssignableValue(type, result)) {
+				throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());
+			}
+			return result;
 		}
 		finally {
 			ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
 		}
 	}
 
+	@Nullable
 	private Object resolveMultipleBeans(DependencyDescriptor descriptor, @Nullable String beanName,
 			@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) {
 
@@ -1500,7 +1513,8 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 					isAutowireCandidate(beanName, mbd, descriptor, getAutowireCandidateResolver())) {
 				// Probably a proxy interfering with target type match -> throw meaningful exception.
 				Object beanInstance = getSingleton(beanName, false);
-				Class<?> beanType = (beanInstance != null ? beanInstance.getClass() : predictBeanType(beanName, mbd));
+				Class<?> beanType = (beanInstance != null && beanInstance.getClass() != NullBean.class) ?
+						beanInstance.getClass() : predictBeanType(beanName, mbd);
 				if (beanType != null && !type.isAssignableFrom(beanType)) {
 					throw new BeanNotOfRequiredTypeException(beanName, type, beanType);
 				}
@@ -1526,7 +1540,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 			}
 			@Override
 			public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory) {
-				return (!ObjectUtils.isEmpty(args) ? beanFactory.getBean(beanName, requiredType, args) :
+				return (!ObjectUtils.isEmpty(args) ? beanFactory.getBean(beanName, args) :
 						super.resolveCandidate(beanName, requiredType, beanFactory));
 			}
 		};
@@ -1615,18 +1629,20 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 		}
 
 		@Override
-		@Nullable
 		public Object getObject() throws BeansException {
 			if (this.optional) {
 				return createOptionalDependency(this.descriptor, this.beanName);
 			}
 			else {
-				return doResolveDependency(this.descriptor, this.beanName, null, null);
+				Object result = doResolveDependency(this.descriptor, this.beanName, null, null);
+				if (result == null) {
+					throw new NoSuchBeanDefinitionException(this.descriptor.getResolvableType());
+				}
+				return result;
 			}
 		}
 
 		@Override
-		@Nullable
 		public Object getObject(final Object... args) throws BeansException {
 			if (this.optional) {
 				return createOptionalDependency(this.descriptor, this.beanName, args);
@@ -1635,10 +1651,14 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 				DependencyDescriptor descriptorToUse = new DependencyDescriptor(descriptor) {
 					@Override
 					public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory) {
-						return ((AbstractBeanFactory) beanFactory).getBean(beanName, requiredType, args);
+						return beanFactory.getBean(beanName, args);
 					}
 				};
-				return doResolveDependency(descriptorToUse, this.beanName, null, null);
+				Object result = doResolveDependency(descriptorToUse, this.beanName, null, null);
+				if (result == null) {
+					throw new NoSuchBeanDefinitionException(this.descriptor.getResolvableType());
+				}
+				return result;
 			}
 		}
 
@@ -1680,6 +1700,16 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 				return doResolveDependency(descriptorToUse, this.beanName, null, null);
 			}
 		}
+
+		@Nullable
+		protected Object getValue() throws BeansException {
+			if (this.optional) {
+				return createOptionalDependency(this.descriptor, this.beanName);
+			}
+			else {
+				return doResolveDependency(this.descriptor, this.beanName, null, null);
+			}
+		}
 	}
 
 
@@ -1695,7 +1725,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 		@Override
 		@Nullable
 		public Object get() throws BeansException {
-			return getObject();
+			return getValue();
 		}
 	}
 

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultSingletonBeanRegistry.java

@@ -73,13 +73,6 @@ import org.springframework.util.StringUtils;
  */
 public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {
 
-	/**
-	 * Internal marker for a null singleton object:
-	 * used as marker value for concurrent Maps (which don't support null values).
-	 */
-	protected static final Object NULL_OBJECT = new Object();
-
-
 	/** Logger available to subclasses */
 	protected final Log logger = LogFactory.getLog(getClass());
 
@@ -125,7 +118,8 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 
 	@Override
 	public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
-		Assert.notNull(beanName, "'beanName' must not be null");
+		Assert.notNull(beanName, "Bean name must not be null");
+		Assert.notNull(singletonObject, "Singleton object must not be null");
 		synchronized (this.singletonObjects) {
 			Object oldObject = this.singletonObjects.get(beanName);
 			if (oldObject != null) {
@@ -142,9 +136,9 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 * @param beanName the name of the bean
 	 * @param singletonObject the singleton object
 	 */
-	protected void addSingleton(String beanName, @Nullable Object singletonObject) {
+	protected void addSingleton(String beanName, Object singletonObject) {
 		synchronized (this.singletonObjects) {
-			this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
+			this.singletonObjects.put(beanName, singletonObject);
 			this.singletonFactories.remove(beanName);
 			this.earlySingletonObjects.remove(beanName);
 			this.registeredSingletons.add(beanName);
@@ -200,7 +194,7 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 				}
 			}
 		}
-		return (singletonObject != NULL_OBJECT ? singletonObject : null);
+		return singletonObject;
 	}
 
 	/**
@@ -211,9 +205,8 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 	 * with, if necessary
 	 * @return the registered singleton object
 	 */
-	@Nullable
 	public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
-		Assert.notNull(beanName, "'beanName' must not be null");
+		Assert.notNull(beanName, "Bean name must not be null");
 		synchronized (this.singletonObjects) {
 			Object singletonObject = this.singletonObjects.get(beanName);
 			if (singletonObject == null) {
@@ -261,7 +254,7 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
 					addSingleton(beanName, singletonObject);
 				}
 			}
-			return (singletonObject != NULL_OBJECT ? singletonObject : null);
+			return singletonObject;
 		}
 	}
 

spring-beans/src/main/java/org/springframework/beans/factory/support/FactoryBeanRegistrySupport.java

@@ -81,8 +81,7 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 */
 	@Nullable
 	protected Object getCachedObjectForFactoryBean(String beanName) {
-		Object object = this.factoryBeanObjectCache.get(beanName);
-		return (object != NULL_OBJECT ? object : null);
+		return this.factoryBeanObjectCache.get(beanName);
 	}
 
 	/**
@@ -94,7 +93,6 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 * @throws BeanCreationException if FactoryBean object creation failed
 	 * @see org.springframework.beans.factory.FactoryBean#getObject()
 	 */
-	@Nullable
 	protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
 		if (factory.isSingleton() && containsSingleton(beanName)) {
 			synchronized (getSingletonMutex()) {
@@ -108,7 +106,7 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 						object = alreadyThere;
 					}
 					else {
-						if (object != null && shouldPostProcess) {
+						if (shouldPostProcess) {
 							try {
 								object = postProcessObjectFromFactoryBean(object, beanName);
 							}
@@ -117,15 +115,15 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 										"Post-processing of FactoryBean's singleton object failed", ex);
 							}
 						}
-						this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
+						this.factoryBeanObjectCache.put(beanName, object);
 					}
 				}
-				return (object != NULL_OBJECT ? object : null);
+				return object;
 			}
 		}
 		else {
 			Object object = doGetObjectFromFactoryBean(factory, beanName);
-			if (object != null && shouldPostProcess) {
+			if (shouldPostProcess) {
 				try {
 					object = postProcessObjectFromFactoryBean(object, beanName);
 				}
@@ -145,7 +143,6 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 * @throws BeanCreationException if FactoryBean object creation failed
 	 * @see org.springframework.beans.factory.FactoryBean#getObject()
 	 */
-	@Nullable
 	private Object doGetObjectFromFactoryBean(final FactoryBean<?> factory, final String beanName)
 			throws BeanCreationException {
 
@@ -174,9 +171,12 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 
 		// Do not accept a null value for a FactoryBean that's not fully
 		// initialized yet: Many FactoryBeans just return null then.
-		if (object == null && isSingletonCurrentlyInCreation(beanName)) {
-			throw new BeanCurrentlyInCreationException(
-					beanName, "FactoryBean which is currently in creation returned null from getObject");
+		if (object == null) {
+			if (isSingletonCurrentlyInCreation(beanName)) {
+				throw new BeanCurrentlyInCreationException(
+						beanName, "FactoryBean which is currently in creation returned null from getObject");
+			}
+			object = new NullBean();
 		}
 		return object;
 	}
@@ -191,7 +191,6 @@ public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanReg
 	 * @return the object to expose
 	 * @throws org.springframework.beans.BeansException if any post-processing failed
 	 */
-	@Nullable
 	protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
 		return object;
 	}

spring-beans/src/main/java/org/springframework/beans/factory/support/NullBean.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2002-2017 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory.support;
+
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.lang.Nullable;
+
+/**
+ * Internal representation of a null bean instance, e.g. for a {@code null} value
+ * returned from {@link FactoryBean#getObject()} or from a factory method.
+ *
+ * <p>Each such null bean is represented by a dedicated {@code NullBean} instance
+ * which are not equal to each other, uniquely differentiating each bean as returned
+ * from all variants of {@link org.springframework.beans.factory.BeanFactory#getBean}.
+ * However, each such instance will return {@code true} for {@code #equals(null)}
+ * and returns "null" from {@code #toString()}, which is how they can be tested
+ * externally (since this class itself is not public).
+ *
+ * @author Juergen Hoeller
+ * @since 5.0
+ */
+final class NullBean {
+
+	NullBean() {
+	}
+
+
+	@Override
+	public boolean equals(@Nullable Object obj) {
+		return (this == obj || obj == null);
+	}
+
+	@Override
+	public int hashCode() {
+		return NullBean.class.hashCode();
+	}
+
+	@Override
+	public String toString() {
+		return "null";
+	}
+
+}

spring-beans/src/main/java/org/springframework/beans/factory/support/SimpleInstantiationStrategy.java

@@ -152,7 +152,11 @@ public class SimpleInstantiationStrategy implements InstantiationStrategy {
 			Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
 			try {
 				currentlyInvokedFactoryMethod.set(factoryMethod);
-				return factoryMethod.invoke(factoryBean, args);
+				Object result = factoryMethod.invoke(factoryBean, args);
+				if (result == null) {
+					result = new NullBean();
+				}
+				return result;
 			}
 			finally {
 				if (priorInvokedFactoryMethod != null) {

spring-beans/src/test/java/org/springframework/beans/factory/FactoryBeanTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -51,8 +51,8 @@ public class FactoryBeanTests {
 	public void testFactoryBeanReturnsNull() throws Exception {
 		DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
 		new XmlBeanDefinitionReader(factory).loadBeanDefinitions(RETURNS_NULL_CONTEXT);
-		Object result = factory.getBean("factoryBean");
-		assertNull(result);
+
+		assertEquals("null", factory.getBean("factoryBean").toString());
 	}
 
 	@Test

spring-beans/src/test/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessorTests.java

@@ -572,8 +572,9 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 	}
 
 	@Test
-	public void testConstructorResourceInjectionWithNull() {
+	public void testConstructorResourceInjectionWithNullFromFactoryBean() {
 		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver());
 		bf.registerResolvableDependency(BeanFactory.class, bf);
 		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
 		bpp.setBeanFactory(bf);
@@ -603,6 +604,42 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 		assertSame(bf, bean.getBeanFactory());
 	}
 
+	@Test
+	public void testConstructorResourceInjectionWithNullFromFactoryMethod() {
+		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver());
+		bf.registerResolvableDependency(BeanFactory.class, bf);
+		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
+		bpp.setBeanFactory(bf);
+		bf.addBeanPostProcessor(bpp);
+		RootBeanDefinition bd = new RootBeanDefinition(ConstructorResourceInjectionBean.class);
+		bd.setScope(RootBeanDefinition.SCOPE_PROTOTYPE);
+		bf.registerBeanDefinition("annotatedBean", bd);
+		RootBeanDefinition tb = new RootBeanDefinition(NullFactoryMethods.class);
+		tb.setFactoryMethodName("createTestBean");
+		bf.registerBeanDefinition("testBean", tb);
+		RootBeanDefinition ntb = new RootBeanDefinition(NullFactoryMethods.class);
+		ntb.setFactoryMethodName("createNestedTestBean");
+		bf.registerBeanDefinition("nestedTestBean", ntb);
+		bf.registerSingleton("nestedTestBean2", new NestedTestBean());
+
+		ConstructorResourceInjectionBean bean = (ConstructorResourceInjectionBean) bf.getBean("annotatedBean");
+		assertNull(bean.getTestBean());
+		assertNull(bean.getTestBean2());
+		assertNull(bean.getTestBean3());
+		assertNull(bean.getTestBean4());
+		assertNull(bean.getNestedTestBean());
+		assertSame(bf, bean.getBeanFactory());
+
+		bean = (ConstructorResourceInjectionBean) bf.getBean("annotatedBean");
+		assertNull(bean.getTestBean());
+		assertNull(bean.getTestBean2());
+		assertNull(bean.getTestBean3());
+		assertNull(bean.getTestBean4());
+		assertNull(bean.getNestedTestBean());
+		assertSame(bf, bean.getBeanFactory());
+	}
+
 	@Test
 	public void testConstructorResourceInjectionWithMultipleCandidates() {
 		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
@@ -756,6 +793,33 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 		bf.destroySingletons();
 	}
 
+	@Test(expected = UnsatisfiedDependencyException.class)
+	public void testSingleConstructorInjectionWithMissingDependency() {
+		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver());
+		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
+		bpp.setBeanFactory(bf);
+		bf.addBeanPostProcessor(bpp);
+		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(SingleConstructorCollectionInjectionBean.class));
+
+		bf.getBean("annotatedBean");
+	}
+
+	@Test(expected = UnsatisfiedDependencyException.class)
+	public void testSingleConstructorInjectionWithNullDependency() {
+		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
+		bf.setAutowireCandidateResolver(new QualifierAnnotationAutowireCandidateResolver());
+		AutowiredAnnotationBeanPostProcessor bpp = new AutowiredAnnotationBeanPostProcessor();
+		bpp.setBeanFactory(bf);
+		bf.addBeanPostProcessor(bpp);
+		bf.registerBeanDefinition("annotatedBean", new RootBeanDefinition(SingleConstructorCollectionInjectionBean.class));
+		RootBeanDefinition tb = new RootBeanDefinition(NullFactoryMethods.class);
+		tb.setFactoryMethodName("createTestBean");
+		bf.registerBeanDefinition("testBean", tb);
+
+		bf.getBean("annotatedBean");
+	}
+
 	@Test
 	public void testConstructorResourceInjectionWithMultipleCandidatesAndFallback() {
 		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
@@ -2634,7 +2698,7 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 
 	public static class ConstructorResourceInjectionBean extends ResourceInjectionBean {
 
-		@Autowired
+		@Autowired(required = false)
 		protected ITestBean testBean3;
 
 		private ITestBean testBean4;
@@ -2643,7 +2707,6 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 
 		private ConfigurableListableBeanFactory beanFactory;
 
-
 		public ConstructorResourceInjectionBean() {
 			throw new UnsupportedOperationException();
 		}
@@ -2653,7 +2716,8 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 		}
 
 		@Autowired
-		public ConstructorResourceInjectionBean(ITestBean testBean4, NestedTestBean nestedTestBean,
+		public ConstructorResourceInjectionBean(@Autowired(required = false) ITestBean testBean4,
+				@Autowired(required = false) NestedTestBean nestedTestBean,
 				ConfigurableListableBeanFactory beanFactory) {
 			this.testBean4 = testBean4;
 			this.nestedTestBean = nestedTestBean;
@@ -2669,7 +2733,7 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 		}
 
 		@Override
-		@Autowired
+		@Autowired(required = false)
 		public void setTestBean2(TestBean testBean2) {
 			super.setTestBean2(testBean2);
 		}
@@ -3802,6 +3866,18 @@ public class AutowiredAnnotationBeanPostProcessorTests {
 	}
 
 
+	public static class NullFactoryMethods {
+
+		public static TestBean createTestBean() {
+			return null;
+		}
+
+		public static NestedTestBean createNestedTestBean() {
+			return null;
+		}
+	}
+
+
 	public static class ProvidedArgumentBean {
 
 		public ProvidedArgumentBean(String[] args) {

spring-beans/src/test/java/org/springframework/beans/factory/config/PropertyPathFactoryBeanTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,6 +38,7 @@ public class PropertyPathFactoryBeanTests {
 
 	private static final Resource CONTEXT = qualifiedResource(PropertyPathFactoryBeanTests.class, "context.xml");
 
+
 	@Test
 	public void testPropertyPathFactoryBeanWithSingletonResult() {
 		DefaultListableBeanFactory xbf = new DefaultListableBeanFactory();
@@ -78,7 +79,7 @@ public class PropertyPathFactoryBeanTests {
 		DefaultListableBeanFactory xbf = new DefaultListableBeanFactory();
 		new XmlBeanDefinitionReader(xbf).loadBeanDefinitions(CONTEXT);
 		assertNull(xbf.getType("tb.spouse.spouse"));
-		assertNull(xbf.getBean("tb.spouse.spouse"));
+		assertEquals("null", xbf.getBean("tb.spouse.spouse").toString());
 	}
 
 	@Test
@@ -92,4 +93,18 @@ public class PropertyPathFactoryBeanTests {
 		assertSame(spouse, tbWithInner.getFriends().iterator().next());
 	}
 
+	@Test
+	public void testPropertyPathFactoryBeanAsNullReference() {
+		DefaultListableBeanFactory xbf = new DefaultListableBeanFactory();
+		new XmlBeanDefinitionReader(xbf).loadBeanDefinitions(CONTEXT);
+		assertNull(xbf.getBean("tbWithNullReference", TestBean.class).getSpouse());
+	}
+
+	@Test
+	public void testPropertyPathFactoryBeanAsInnerNull() {
+		DefaultListableBeanFactory xbf = new DefaultListableBeanFactory();
+		new XmlBeanDefinitionReader(xbf).loadBeanDefinitions(CONTEXT);
+		assertNull(xbf.getBean("tbWithInnerNull", TestBean.class).getSpouse());
+	}
+
 }

spring-beans/src/test/java/org/springframework/beans/factory/xml/FactoryMethodTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -91,8 +91,7 @@ public class FactoryMethodTests {
 		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(xbf);
 		reader.loadBeanDefinitions(new ClassPathResource("factory-methods.xml", getClass()));
 
-		FactoryMethods fm = (FactoryMethods) xbf.getBean("null");
-		assertNull(fm);
+		assertEquals("null", xbf.getBean("null").toString());
 
 		try {
 			xbf.getBean("nullWithProperty");

spring-beans/src/test/resources/org/springframework/beans/factory/config/PropertyPathFactoryBeanTests-context.xml

@@ -57,6 +57,16 @@
 		<property name="friends">
 			<bean name="otb.spouse" class="org.springframework.beans.factory.config.PropertyPathFactoryBean"/>
 		</property>
-  </bean>
+	</bean>
+
+	<bean id="tbWithNullReference" class="org.springframework.tests.sample.beans.TestBean">
+		<property name="spouse" ref="tb.spouse.spouse"/>
+	</bean>
+
+	<bean id="tbWithInnerNull" class="org.springframework.tests.sample.beans.TestBean">
+		<property name="spouse">
+			<bean name="tb.spouse.spouse" class="org.springframework.beans.factory.config.PropertyPathFactoryBean"/>
+		</property>
+	</bean>
 
 </beans>

spring-context/src/main/java/org/springframework/cache/support/NullValue.java

@@ -18,6 +18,8 @@ package org.springframework.cache.support;
 
 import java.io.Serializable;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Simple serializable class that serves as a {@code null} replacement
  * for cache stores which otherwise do not support {@code null} values.
@@ -46,4 +48,20 @@ public final class NullValue implements Serializable {
 		return INSTANCE;
 	}
 
+
+	@Override
+	public boolean equals(@Nullable Object obj) {
+		return (this == obj || obj == null);
+	}
+
+	@Override
+	public int hashCode() {
+		return NullValue.class.hashCode();
+	}
+
+	@Override
+	public String toString() {
+		return "null";
+	}
+
 }

spring-context/src/main/java/org/springframework/context/support/SimpleThreadScope.java

@@ -72,7 +72,6 @@ public class SimpleThreadScope implements Scope {
 		Object scopedObject = scope.get(name);
 		if (scopedObject == null) {
 			scopedObject = objectFactory.getObject();
-			Assert.state(scopedObject != null, "Scoped object resolved to null");
 			scope.put(name, scopedObject);
 		}
 		return scopedObject;

spring-context/src/main/java/org/springframework/jmx/export/MBeanExporter.java

@@ -508,7 +508,7 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	//---------------------------------------------------------------------
 
 	/**
-	 * Registers the defined beans with the {@link MBeanServer}.
+	 * Register the defined beans with the {@link MBeanServer}.
 	 * <p>Each bean is exposed to the {@code MBeanServer} via a
 	 * {@code ModelMBean}. The actual implemetation of the
 	 * {@code ModelMBean} interface used depends on the implementation of
@@ -566,7 +566,7 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	}
 
 	/**
-	 * Registers an individual bean with the {@link #setServer MBeanServer}.
+	 * Register an individual bean with the {@link #setServer MBeanServer}.
 	 * <p>This method is responsible for deciding <strong>how</strong> a bean
 	 * should be exposed to the {@code MBeanServer}. Specifically, if the
 	 * supplied {@code mapValue} is the name of a bean that is configured
@@ -579,15 +579,13 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	 * @param mapValue the value configured for this bean in the beans map;
 	 * may be either the {@code String} name of a bean, or the bean itself
 	 * @param beanKey the key associated with this bean in the beans map
-	 * @return the {@code ObjectName} under which the resource was registered,
-	 * or {@code null} if the actual resource was {@code null} as well
+	 * @return the {@code ObjectName} under which the resource was registered
 	 * @throws MBeanExportException if the export failed
 	 * @see #setBeans
 	 * @see #registerBeanInstance
 	 * @see #registerLazyInit
 	 */
-	@Nullable
-	protected ObjectName registerBeanNameOrInstance(@Nullable Object mapValue, String beanKey) throws MBeanExportException {
+	protected ObjectName registerBeanNameOrInstance(Object mapValue, String beanKey) throws MBeanExportException {
 		try {
 			if (mapValue instanceof String) {
 				// Bean name pointing to a potentially lazy-init bean in the factory.
@@ -607,7 +605,7 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 					return objectName;
 				}
 			}
-			else if (mapValue != null) {
+			else {
 				// Plain bean instance -> register it directly.
 				if (this.beanFactory != null) {
 					Map<String, ?> beansOfSameType =
@@ -623,9 +621,6 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 				}
 				return registerBeanInstance(mapValue, beanKey);
 			}
-			else {
-				return null;
-			}
 		}
 		catch (Throwable ex) {
 			throw new UnableToRegisterMBeanException(
@@ -634,14 +629,14 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	}
 
 	/**
-	 * Replaces any bean names used as keys in the {@code NotificationListener}
+	 * Replace any bean names used as keys in the {@code NotificationListener}
 	 * mappings with their corresponding {@code ObjectName} values.
 	 * @param beanName the name of the bean to be registered
 	 * @param objectName the {@code ObjectName} under which the bean will be registered
 	 * with the {@code MBeanServer}
 	 */
-	private void replaceNotificationListenerBeanNameKeysIfNecessary(String beanName, @Nullable ObjectName objectName) {
-		if (objectName != null && this.notificationListeners != null) {
+	private void replaceNotificationListenerBeanNameKeysIfNecessary(String beanName, ObjectName objectName) {
+		if (this.notificationListeners != null) {
 			for (NotificationListenerBean notificationListener : this.notificationListeners) {
 				notificationListener.replaceObjectName(beanName, objectName);
 			}
@@ -656,12 +651,7 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	 * @return the {@code ObjectName} under which the bean was registered
 	 * with the {@code MBeanServer}
 	 */
-	@Nullable
-	private ObjectName registerBeanInstance(@Nullable Object bean, String beanKey) throws JMException {
-		if (bean == null) {
-			return null;
-		}
-
+	private ObjectName registerBeanInstance(Object bean, String beanKey) throws JMException {
 		ObjectName objectName = getObjectName(bean, beanKey);
 		Object mbeanToExpose = null;
 		if (isMBean(bean.getClass())) {
@@ -695,7 +685,7 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 	}
 
 	/**
-	 * Registers beans that are configured for lazy initialization with the
+	 * Register beans that are configured for lazy initialization with the
 	 * {@code MBeanServer} indirectly through a proxy.
 	 * @param beanName the name of the bean in the {@code BeanFactory}
 	 * @param beanKey the key associated with this bean in the beans map
@@ -890,7 +880,13 @@ public class MBeanExporter extends MBeanRegistrationSupport implements MBeanExpo
 					Class<?> beanClass = this.beanFactory.getType(beanName);
 					if (beanClass != null && callback.include(beanClass, beanName)) {
 						boolean lazyInit = isBeanDefinitionLazyInit(this.beanFactory, beanName);
-						Object beanInstance = (!lazyInit ? this.beanFactory.getBean(beanName) : null);
+						Object beanInstance = null;
+						if (!lazyInit) {
+							beanInstance = this.beanFactory.getBean(beanName);
+							if (!beanClass.isInstance(beanInstance)) {
+								continue;
+							}
+						}
 						if (!ScopedProxyUtils.isScopedTarget(beanName) && !beans.containsValue(beanName) &&
 								(beanInstance == null ||
 										!CollectionUtils.containsInstance(beans.values(), beanInstance))) {

spring-context/src/test/java/org/springframework/cache/interceptor/CacheResolverCustomizationTests.java

@@ -58,14 +58,14 @@ public class CacheResolverCustomizationTests {
 
 
 	@Before
-	public void setUp() {
+	public void setup() {
 		ApplicationContext context = new AnnotationConfigApplicationContext(Config.class);
 		this.cacheManager = context.getBean("cacheManager", CacheManager.class);
 		this.anotherCacheManager = context.getBean("anotherCacheManager", CacheManager.class);
-
 		this.simpleService = context.getBean(SimpleService.class);
 	}
 
+
 	@Test
 	public void noCustomization() {
 		Cache cache = this.cacheManager.getCache("default");
@@ -162,12 +162,6 @@ public class CacheResolverCustomizationTests {
 			return CacheTestUtils.createSimpleCacheManager("default", "primary", "secondary");
 		}
 
-		@Override
-		@Bean
-		public KeyGenerator keyGenerator() {
-			return null;
-		}
-
 		@Bean
 		public CacheManager anotherCacheManager() {
 			return CacheTestUtils.createSimpleCacheManager("default", "primary", "secondary");

spring-context/src/test/java/org/springframework/context/annotation/CommonAnnotationBeanPostProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -114,7 +114,7 @@ public class CommonAnnotationBeanPostProcessorTests {
 		rbd.setFactoryMethodName("create");
 		bf.registerBeanDefinition("bean", rbd);
 
-		assertNull(bf.getBean("bean"));
+		assertEquals("null", bf.getBean("bean").toString());
 		bf.destroySingletons();
 	}
 

spring-context/src/test/java/org/springframework/context/support/GenericApplicationContextTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,13 +30,6 @@ import static org.junit.Assert.*;
  */
 public class GenericApplicationContextTests {
 
-	@Test
-	public void nullBeanRegistration() {
-		DefaultListableBeanFactory bf = new DefaultListableBeanFactory();
-		bf.registerSingleton("nullBean", null);
-		new GenericApplicationContext(bf).refresh();
-	}
-
 	@Test
 	public void getBeanForClass() {
 		GenericApplicationContext ac = new GenericApplicationContext();

spring-messaging/src/main/java/org/springframework/messaging/simp/SimpSessionScope.java

@@ -19,7 +19,6 @@ package org.springframework.messaging.simp;
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.config.Scope;
 import org.springframework.lang.Nullable;
-import org.springframework.util.Assert;
 
 /**
  * A {@link Scope} implementation exposing the attributes of a SiMP session
@@ -44,7 +43,6 @@ public class SimpSessionScope implements Scope {
 			scopedObject = simpAttributes.getAttribute(name);
 			if (scopedObject == null) {
 				scopedObject = objectFactory.getObject();
-				Assert.state(scopedObject != null, "Scoped object resolved to null");
 				simpAttributes.setAttribute(name, scopedObject);
 			}
 			return scopedObject;

spring-tx/src/main/java/org/springframework/transaction/support/SimpleTransactionScope.java

@@ -54,7 +54,6 @@ public class SimpleTransactionScope implements Scope {
 		Object scopedObject = scopedObjects.scopedInstances.get(name);
 		if (scopedObject == null) {
 			scopedObject = objectFactory.getObject();
-			Assert.state(scopedObject != null, "Scoped object resolved to null");
 			scopedObjects.scopedInstances.put(name, scopedObject);
 		}
 		return scopedObject;

spring-web/src/main/java/org/springframework/web/context/request/AbstractRequestAttributesScope.java

@@ -19,7 +19,6 @@ package org.springframework.web.context.request;
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.beans.factory.config.Scope;
 import org.springframework.lang.Nullable;
-import org.springframework.util.Assert;
 
 /**
  * Abstract {@link Scope} implementation that reads from a particular scope
@@ -44,7 +43,6 @@ public abstract class AbstractRequestAttributesScope implements Scope {
 		Object scopedObject = attributes.getAttribute(name, getScope());
 		if (scopedObject == null) {
 			scopedObject = objectFactory.getObject();
-			Assert.state(scopedObject != null, "Scoped object resolved to null");
 			attributes.setAttribute(name, scopedObject, getScope());
 			// Retrieve object again, registering it for implicit session attribute updates.
 			// As a bonus, we also allow for potential decoration at the getAttribute level.

spring-web/src/main/java/org/springframework/web/context/support/ServletContextScope.java

@@ -68,7 +68,6 @@ public class ServletContextScope implements Scope, DisposableBean {
 		Object scopedObject = this.servletContext.getAttribute(name);
 		if (scopedObject == null) {
 			scopedObject = objectFactory.getObject();
-			Assert.state(scopedObject != null, "Scoped object resolved to null");
 			this.servletContext.setAttribute(name, scopedObject);
 		}
 		return scopedObject;