code: public boolean isMarshallable(Class<?> type) {
        MarshallingType marshallingType = typeHints.get(type);
        if (marshallingType != null) {
           Boolean marshallable = marshallingType.isMarshallable;
           return marshallable != null ? marshallable.booleanValue() : false;
        }
  
        return false;
     }
docs: Returns whether a type can be serialized. In order for a type to be
  considered marshallable, the type must have been marked as marshallable
  using the {@link #markMarshallable(Class, boolean)} method earlier,
  passing true as parameter. If a type has not yet been marked as
  marshallable, this method will return false.