ServletRequestMethodArgumentResolver passes null references through (again)

Issue: SPR-15214

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ServletRequestMethodArgumentResolver.java

@@ -121,7 +121,7 @@ public class ServletRequestMethodArgumentResolver implements HandlerMethodArgume
 	private Object resolveArgument(Class<?> paramType, HttpServletRequest request) throws IOException {
 		if (HttpSession.class.isAssignableFrom(paramType)) {
 			HttpSession session = request.getSession();
-			if (!paramType.isInstance(session)) {
+			if (session != null && !paramType.isInstance(session)) {
 				throw new IllegalStateException(
 						"Current session is not of type [" + paramType.getName() + "]: " + session);
 			}
@@ -129,7 +129,7 @@ public class ServletRequestMethodArgumentResolver implements HandlerMethodArgume
 		}
 		else if (getPushBuilderMethod != null && getPushBuilderMethod.getReturnType().isAssignableFrom(paramType)) {
 			Object pushBuilder = ReflectionUtils.invokeMethod(getPushBuilderMethod, request);
-			if (!paramType.isInstance(pushBuilder)) {
+			if (pushBuilder != null && !paramType.isInstance(pushBuilder)) {
 				throw new IllegalStateException(
 						"Current push builder is not of type [" + paramType.getName() + "]: " + pushBuilder);
 			}
@@ -137,7 +137,7 @@ public class ServletRequestMethodArgumentResolver implements HandlerMethodArgume
 		}
 		else if (InputStream.class.isAssignableFrom(paramType)) {
 			InputStream inputStream = request.getInputStream();
-			if (!paramType.isInstance(inputStream)) {
+			if (inputStream != null && !paramType.isInstance(inputStream)) {
 				throw new IllegalStateException(
 						"Request input stream is not of type [" + paramType.getName() + "]: " + inputStream);
 			}
@@ -145,7 +145,7 @@ public class ServletRequestMethodArgumentResolver implements HandlerMethodArgume
 		}
 		else if (Reader.class.isAssignableFrom(paramType)) {
 			Reader reader = request.getReader();
-			if (!paramType.isInstance(reader)) {
+			if (reader != null && !paramType.isInstance(reader)) {
 				throw new IllegalStateException(
 						"Request body reader is not of type [" + paramType.getName() + "]: " + reader);
 			}
@@ -153,7 +153,7 @@ public class ServletRequestMethodArgumentResolver implements HandlerMethodArgume
 		}
 		else if (Principal.class.isAssignableFrom(paramType)) {
 			Principal userPrincipal = request.getUserPrincipal();
-			if (!paramType.isInstance(userPrincipal)) {
+			if (userPrincipal != null && !paramType.isInstance(userPrincipal)) {
 				throw new IllegalStateException(
 						"Current user principal is not of type [" + paramType.getName() + "]: " + userPrincipal);
 			}

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ServletRequestMethodArgumentResolverTests.java

@@ -62,7 +62,7 @@ public class ServletRequestMethodArgumentResolverTests {
 
 
 	@Before
-	public void setUp() throws Exception {
+	public void setup() throws Exception {
 		method = getClass().getMethod("supportedParams", ServletRequest.class, MultipartRequest.class,
 				HttpSession.class, Principal.class, Locale.class, InputStream.class, Reader.class,
 				WebRequest.class, TimeZone.class, ZoneId.class, HttpMethod.class);
@@ -112,6 +112,15 @@ public class ServletRequestMethodArgumentResolverTests {
 		assertSame("Invalid result", principal, result);
 	}
 
+	@Test
+	public void principalAsNull() throws Exception {
+		MethodParameter principalParameter = new MethodParameter(method, 3);
+		assertTrue("Principal not supported", resolver.supportsParameter(principalParameter));
+
+		Object result = resolver.resolveArgument(principalParameter, null, webRequest, null);
+		assertNull("Invalid result", result);
+	}
+
 	@Test
 	public void locale() throws Exception {
 		Locale locale = Locale.ENGLISH;