@Override
    protected final boolean equalsExpression(ExpressionNode obj) {
        AggregationResult rhs = (AggregationResult)obj;
        if (!equals(expression, rhs.expression)) {
            return false;
        }
        if (tag != rhs.tag) {
            return false;
        }
        if (!equalsAggregation(rhs)) {
            return false;
        }
        return true;
    }
Mmust be implemented by subclasses to support merge. It is called as the {@link
#merge(AggregationResult)} method is invoked.

@param result the result to merge with
searchlib/src/main/java/com/yahoo/searchlib/aggregation/AggregationResult.java