@Override
  public boolean hasPeriod() {
    checkHolderIsInitialized();
    return period != null;
  }
@Test
  public void hasPeriod_throws_ISE_if_not_initialized() {
    assertThatThrownBy(() -> underTest.hasPeriod())
      .isInstanceOf(IllegalStateException.class)
      .hasMessage("Period have not been initialized yet");
  }