fixed GenericTypeResolver to consistently return null if not resolvable (SPR-8698)

org.springframework.core/src/main/java/org/springframework/core/GenericTypeResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2011 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.
@@ -41,7 +41,6 @@ import org.springframework.util.Assert;
  * @author Rob Harrop
  * @since 2.5.2
  * @see GenericCollectionTypeResolver
- * @see JdkVersion
  */
 public abstract class GenericTypeResolver {
 
@@ -175,7 +174,7 @@ public abstract class GenericTypeResolver {
 				return doResolveTypeArguments(ownerClass, (Class) rawType, genericIfc);
 			}
 		}
-		else if (genericIfc.isAssignableFrom((Class) ifc)) {
+		else if (ifc != null && genericIfc.isAssignableFrom((Class) ifc)) {
 			return doResolveTypeArguments(ownerClass, (Class) ifc, genericIfc);
 		}
 		return null;

org.springframework.core/src/test/java/org/springframework/core/GenericTypeResolverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2010 the original author or authors.
+ * Copyright 2002-2011 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.
@@ -18,9 +18,10 @@ package org.springframework.core;
 
 import java.util.Collection;
 
-import static org.junit.Assert.*;
 import org.junit.Test;
 
+import static org.junit.Assert.*;
+
 /**
  * @author Juergen Hoeller
  */
@@ -46,6 +47,12 @@ public class GenericTypeResolverTests {
 		assertEquals(Collection.class, GenericTypeResolver.resolveTypeArgument(MyCollectionSuperclassType.class, MySuperclassType.class));
 	}
 
+	@Test
+	public void testNullIfNotResolvable() {
+		GenericClass<String> obj = new GenericClass<String>();
+		assertNull(GenericTypeResolver.resolveTypeArgument(obj.getClass(), GenericClass.class));
+	}
+
 
 	public interface MyInterfaceType<T> {
 	}
@@ -66,4 +73,7 @@ public class GenericTypeResolverTests {
 	public class MyCollectionSuperclassType extends MySuperclassType<Collection<String>> {
 	}
 
+	static class GenericClass<T> {
+	}
+
 }