@Override
    public RawBucket getBucket(int i) {
        return (RawBucket)getArg(i + 1);
    }
Constructs a new instance of this class.

@param exp  The expression to evaluate, must evaluate to a string.
@param arg1 The compulsory bucket.
@param argN The optional buckets.
container-search/src/main/java/com/yahoo/search/grouping/request/RawPredefined.java