docs: @Override protected Response serve() {
      if( src_key == null ) return RequestServer._http404.serve();
      Vec v = src_key.anyVec();
      if (v.isEnum()) {
        map = Arrays.asList(v.domain()).indexOf(str);
      } else if (v.masterVec() != null && v.masterVec().isEnum()) {
        map = Arrays.asList(v.masterVec().domain()).indexOf(str);
      } else {
        map = -1;
      }
      return Response.done(this);
    }