#1379 - Proper type resolution for CollectionModel post-processing.

CollectionModelProcessorWrapper erroneously returned a raw type in case a CollectionModel type assignment check failed which rendered the element type verification to always match as it's effectively compared against Object.

We're now returning null to rather proceed with the next candidate type.

src/main/java/org/springframework/hateoas/server/mvc/RepresentationModelProcessorInvoker.java

@@ -429,6 +429,7 @@ public class RepresentationModelProcessorInvoker {
 		 * @param superType must not be {@literal null}.
 		 * @return
 		 */
+		@Nullable
 		private static ResolvableType getSuperType(ResolvableType source, Class<?> superType) {
 
 			Class<?> rawType = source.getRawClass();
@@ -449,7 +450,7 @@ public class RepresentationModelProcessorInvoker {
 				}
 			}
 
-			return ResolvableType.forClass(superType);
+			return null;
 		}
 	}