@Override
  public void setResult(CeTaskResult taskResult) {
    requireNonNull(taskResult, "taskResult can not be null");
    checkState(this.result == null, "CeTaskResult has already been set in the holder");
    this.result = taskResult;
  }
@Test
  public void setResult_throws_NPE_if_CeTaskResult_argument_is_null() {
    assertThatThrownBy(() -> underTest.setResult(null))
      .isInstanceOf(NullPointerException.class)
      .hasMessage("taskResult can not be null");
  }