code: function rethrow(error) {
          if (filterTree && error instanceof filterTree.Error) {
              alert(error);
              reveal(error);
          } else if (error) {
              throw error;
          }
  
          return error;
      }
docs: Can be used in two ways:
  1. Call from a catch block
  2. Call with result of a filter tree invalid call (with quiet validation)
  @param {Error|FilterTreeError} error
  @returns {FilterTreeError} Will return on `FilterTreeError`; otherwise throws `Error`.