public static Builder newBuilder() {
    return new Builder();
  }
@Test
  public void build_fails_with_NPE_if_source_is_null() {
    AuthenticationException.Builder builder = AuthenticationException.newBuilder()
        .setLogin("login")
        .setMessage("message");

    assertThatThrownBy(builder::build)
      .isInstanceOf(NullPointerException.class)
      .hasMessage("source can't be null");
  }