public boolean isValidField(final String fieldName) {
        if (config == null) {
            return false;
        } else if (config.getFields() == null) {
            return false;
        } else if (config.getFields().size() == 0) {
            return false;
        } else {
            return config.getFields().contains(new StatisticField(fieldName));
        }
    }
@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