code: @Override
      public XBELCitation convert(Citation source) {
          if (source == null) {
              return null;
          }
  
          XBELCitation xc = new XBELCitation();
  
          xc.setDate(source.getDate());
          xc.setComment(source.getComment());
          xc.setReference(source.getReference());
          xc.setName(source.getName());
  
          org.openbel.framework.common.enums.CitationType type = source.getType();
          if (type != null) {
              CitationType ct = CitationType.fromValue(type.getDisplayValue());
              xc.setType(ct);
          }
  
          List<String> authors = source.getAuthors();
          if (hasItems(authors)) {
              AuthorGroup ag = new AuthorGroup();
              List<String> xauthors = ag.getAuthor();
              for (final String author : authors) {
                  xauthors.add(author);
              }
              xc.setAuthorGroup(ag);
          }
  
          return xc;
      }
docs: {@inheritDoc}