@Override
  public Iterable<Duplication> getDuplications(Component file) {
    checkFileComponentArgument(file);

    Collection<Duplication> res = this.duplications.asMap().get(file.getKey());
    if (res == null) {
      return Collections.emptyList();
    }
    return res;
  }
@Test
  public void getDuplications_throws_NPE_if_Component_argument_is_null() {
    assertThatThrownBy(() -> underTest.getDuplications(null))
      .isInstanceOf(NullPointerException.class)
      .hasMessage("file can not be null");
  }