public static Combine.CombineFn<Boolean, ?, Long> combineFn() {
    return new CountIfFn();
  }
@Test
  public void testReturnsAccumulatorUnchangedForNullInput() {
    Combine.CombineFn countIfFn = CountIf.combineFn();
    long[] accumulator = (long[]) countIfFn.addInput(countIfFn.createAccumulator(), null);

    assertEquals(0L, accumulator[0]);
  }