@Override
    protected boolean equalsAggregation(AggregationResult obj) {
        // obj is assumed to always be of correct type.
        ExpressionCountAggregationResult other = (ExpressionCountAggregationResult) obj;
        return sketch.equals(other.sketch);
    }
@return The unique count estimated by the HyperLogLog algorithm.
searchlib/src/main/java/com/yahoo/searchlib/aggregation/ExpressionCountAggregationResult.java