public void setUuids(Set<String> uuids) {
    requireNonNull(uuids, "Uuids cannot be null");
    checkState(this.uuids == null, "Uuids have already been initialized");
    this.uuids = new HashSet<>(uuids);
  }
@Test
  public void fail_with_NPE_when_setting_null_uuids() {
    assertThatThrownBy(() -> sut.setUuids(null))
      .isInstanceOf(NullPointerException.class)
      .hasMessage("Uuids cannot be null");
  }