public Parser blankWhenZero() {
        if (blankWhenZeroParser == null) {
           FutureParser future = scoped("blankWhenZero");
           blankWhenZeroParser = future;
           future.setParser(
               sequence(
                   token("BLANK"),
                   optional(
                       token("WHEN")
                   ),
                   zero()
               )
           );
        }

        return blankWhenZeroParser;
    }