@Override
    public void selectMembers(ObjectPredicate predicate, ObjectOperation operation) {
        select(defaultExp, predicate, operation);
        for (Expression exp : cases.values()) {
            select(exp, predicate, operation);
        }
    }
The default expression, or null if none
indexinglanguage/src/main/java/com/yahoo/vespa/indexinglanguage/expressions/SwitchExpression.java