@Override
  public VarianceAccumulator addInput(VarianceAccumulator currentVariance, T rawInput) {

    if (rawInput == null) {
      return currentVariance;
    }

    return currentVariance.combineWith(
        VarianceAccumulator.ofSingleElement(SqlFunctions.toBigDecimal(rawInput)));
  }
@Test
  public void testReturnsAccumulatorUnchangedForNullInput() {
    VarianceAccumulator accumulator = newVarianceAccumulator(ZERO, BigDecimal.ONE, BigDecimal.TEN);

    assertEquals(accumulator, varianceFn.addInput(accumulator, null));
  }