code: @Override
      public XBELExternalAnnotationDefinition convert(AnnotationDefinition t) {
          if (t == null || t.getURL() == null) {
              return null;
          }
  
          XBELExternalAnnotationDefinition dest =
                  new XBELExternalAnnotationDefinition();
  
          String id = t.getId();
          String url = t.getURL();
  
          dest.setId(id);
          dest.setUrl(url);
  
          return dest;
      }
docs: {@inheritDoc}