@Override
    public BucketSpec apply(final Grouping grouping) {
        return Values.builder()
                .field(grouping.requestedField().name())
                .type(Values.NAME)
                .limit(grouping.limit())
                .build();
    }
@Test
    void throwsNullPointerExceptionOnNullGrouping() {
        assertThrows(NullPointerException.class, () -> toTest.apply(null));
    }