code: @Override
      public String handle(final Object value) {
          final StringBuilder s = new StringBuilder();
          if (value instanceof List) {
              final List<?> l = (List<?>) value;
              for (final Object o : l) {
                  if (s.length() > 0) {
                      s.append(',');
                  }
                  s.append(o.toString());
              }
          } else {
              s.append(value);
          }
          return s.toString();
      }
docs: Converts the list to a comma separated representation.
  
  @return a comma separated list of values
  @see fr.dudie.nominatim.client.request.paramhelper.QueryParameterSerializer#handle(java.lang.Object)