public boolean addMask(final CustomRollUpMask mask) {
            final MaskHolder holder = new MaskHolder(idCounter++, mask);

            return super.add(holder);
        }
Extension of ArrayList that adds an ID value to each
{@link CustomRollUpMask} object added to it
stroom-statistics/stroom-statistics-client/src/main/java/stroom/statistics/impl/hbase/client/presenter/StroomStatsStoreCustomMaskListPresenter.java