code: function (props, key) {
          if (props[key]) {
              return;
          }
          props[key] = {
              configurable: true,
              enumerable: true,
              writable: true,
              value: function () {
                  var error = this[__symbol__('error')];
                  var errorMethod = (error && error[key]) || this[key];
                  if (errorMethod) {
                      return errorMethod.apply(error, arguments);
                  }
              }
          };
      }
docs: fix #595, create property descriptor for error method properties