public boolean isRollUpCombinationSupported(final Set<String> rolledUpFieldNames) {
        if (rolledUpFieldNames == null || rolledUpFieldNames.isEmpty()) {
            return true;
        }

        if (getRollUpType().equals(StatisticRollUpType.NONE)) {
            return false;
        }

        if (getRollUpType().equals(StatisticRollUpType.ALL)) {
            return true;
        }

        // rolledUpFieldNames not empty if we get here

        if (config == null) {
            throw new RuntimeException("isRollUpCombinationSupported called with non-empty list but data source " +
                                       "has no statistic fields or custom roll up masks");
        }

        return config.isRollUpCombinationSupported(rolledUpFieldNames);
    }
@return A new builder for creating a {@link DocRef} for this document's type.
stroom-core-shared/src/main/java/stroom/statistics/impl/sql/shared/StatisticStoreDoc.java