return null;
          }

          @Override
          boolean isDone() {
            return false;
          }

          @Override
          String toPendingString() {
            return "";
          }

          @Override
          void afterRanInterruptiblySuccess(@Nullable Void result) {}

          @Override

  abstract void afterRanInterruptiblySuccess(T result);

  abstract void afterRanInterruptiblyFailure(Throwable error);

  final void interruptTask() {}

  abstract String toPendingString();