public BucketValue getBucket(int i) {
        return (BucketValue)getArg(i + 1);
    }
Returns the bucket at the given index.

@param i The index of the bucket to return.
@return The bucket at the given index.
@throws IndexOutOfBoundsException If the index is out of range.
container-search/src/main/java/com/yahoo/search/grouping/request/PredefinedFunction.java