@Test public void testCountingDistinct_distinctEntries_withNulls() {

  assertThat(BiStream.of(1, "one", 1, null).collect(BiCollectors.countingDistinct()))
      .isEqualTo(2);
  assertThat(BiStream.of(1, "one", null, "one").collect(BiCollectors.countingDistinct()))
      .isEqualTo(2);
  assertThat(BiStream.of(1, "one", null, null).collect(BiCollectors.countingDistinct()))
      .isEqualTo(2);
}