code: @Override
      boolean hasContent(LessExtendMap lessExtends ) {
          if( output.length() == 0 ) {
              return false;
          }
          if( !isConcatExtents ) {
              isConcatExtents = true;
              selectors = lessExtends.concatenateExtends( selectors, isReference );
          }
          return selectors.length > 0;
      }
docs: {@inheritDoc}