Polish type prediction for generic factory methods

- Now avoiding NullPointerExceptions in GenericTypeResolver's
   resolveReturnTypeForGenericMethod() in case the supplied ClassLoader
   is null.
 - AutowireUtils.resolveReturnTypeForFactoryMethod() now properly
   asserts that the supplied ClassLoader is not null.
 - Fixed copy-n-paste errors in Javadoc for
   AutowireUtils.resolveReturnTypeForFactoryMethod().

Issue: SPR-10411

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

@@ -164,7 +164,7 @@ public abstract class GenericTypeResolver {
 							if (arg instanceof Class) {
 								return (Class<?>) arg;
 							}
-							else if (arg instanceof String) {
+							else if (arg instanceof String && classLoader != null) {
 								try {
 									return classLoader.loadClass((String) arg);
 								}