@Override
    public Object merge(T mergingValue, T existingValue) {
        if (existingValue == null) {
            return null;
        }
        return existingValue.getRawValue();
    }
@Test
    public void merge_bothValuesNull() {
        MapMergeTypes existing = mergingValueWithGivenValue(null);
        MapMergeTypes merging = mergingValueWithGivenValue(null);

        assertNull(mergePolicy.merge(merging, existing));
    }