@Override
    public SumAggregationResult clone() {
        SumAggregationResult obj = (SumAggregationResult)super.clone();
        if (sum != null) {
            obj.sum = (SingleResultNode)sum.clone();
        }
        return obj;
    }
Sets the sum of all results in this.

@param sum The sum to set.
@return This, to allow chaining.
searchlib/src/main/java/com/yahoo/searchlib/aggregation/SumAggregationResult.java