@Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + id;
            return result;
        }
Wrap the mask with an ID value that can be used for equality checks in
the UI, to allow multiple rows with the same check box values
stroom-statistics/stroom-statistics-client/src/main/java/stroom/statistics/impl/sql/client/presenter/StatisticsCustomMaskListPresenter.java