Method setError

bolt/exec/tests/utils/Cursor.cpp:488–493

      // When next is returned from task as a null pointer.
      if (!future.valid()) {
        BOLT_CHECK(!task_->isRunning() || !noMoreSplits_);
        return false;
      }
      // Task is blocked for some reason. Wait and try again.
      BOLT_CHECK_NULL(next);
      future.wait();
    }
  };