Added subtype registration

src/main/java/org/gcube/informationsystem/serialization/ElementMapper.java

@@ -146,6 +146,7 @@ public class ElementMapper {
 		module.setAbstractTypes(resolver);
 
 		mapper.registerModule(module);
+		mapper.registerSubtypes(interfaceClz);
 	}
 	
 	public static <El extends Element> void registerSubtype(Class<El> clz) {