Restore non-null check for requiredType in BeanFactory methods

Beginning with Spring Framework 5.0, non-null checks for the
requiredType in the following methods were inadvertently removed with
the internal switch to ResolvableType.forRawClass(requiredType).

- BeanFactory.getBean(Class<T>, Object...)
- BeanFactory.getBeanProvider(Class<T>)
- AutowireCapableBeanFactory.resolveNamedBean(Class<T>)

This commit restores those non-null checks.

Closes gh-23045

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

@@ -208,7 +208,7 @@ public interface BeanFactory {
 	<T> T getBean(Class<T> requiredType, Object... args) throws BeansException;
 
 	/**
-	 * Return an provider for the specified bean, allowing for lazy on-demand retrieval
+	 * Return a provider for the specified bean, allowing for lazy on-demand retrieval
 	 * of instances, including availability and uniqueness options.
 	 * @param requiredType type the bean must match; can be an interface or superclass
 	 * @return a corresponding provider handle
@@ -218,7 +218,7 @@ public interface BeanFactory {
 	<T> ObjectProvider<T> getBeanProvider(Class<T> requiredType);
 
 	/**
-	 * Return an provider for the specified bean, allowing for lazy on-demand retrieval
+	 * Return a provider for the specified bean, allowing for lazy on-demand retrieval
 	 * of instances, including availability and uniqueness options.
 	 * @param requiredType type the bean must match; can be a generic type declaration.
 	 * Note that collection types are not supported here, in contrast to reflective

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

@@ -340,6 +340,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	@SuppressWarnings("unchecked")
 	@Override
 	public <T> T getBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {
+		Assert.notNull(requiredType, "Required type must not be null");
 		Object resolved = resolveBean(ResolvableType.forRawClass(requiredType), args, false);
 		if (resolved == null) {
 			throw new NoSuchBeanDefinitionException(requiredType);
@@ -349,6 +350,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 
 	@Override
 	public <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType) throws BeansException {
+		Assert.notNull(requiredType, "Required type must not be null");
 		return getBeanProvider(ResolvableType.forRawClass(requiredType));
 	}
 
@@ -1080,6 +1082,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 
 	@Override
 	public <T> NamedBeanHolder<T> resolveNamedBean(Class<T> requiredType) throws BeansException {
+		Assert.notNull(requiredType, "Required type must not be null");
 		NamedBeanHolder<T> namedBean = resolveNamedBean(ResolvableType.forRawClass(requiredType), null, false);
 		if (namedBean != null) {
 			return namedBean;