presto-main/src/main/java/io/prestosql/sql/planner/optimizations/OptimizeMixedDistinctAggregations.java/OptimizeMixedDistinctAggregations/createIfExpression
class OptimizeMixedDistinctAggregations:        private static IfExpression createIfExpression(Expression left, Expression right, ComparisonExpression.Operator operator, Expression result, Type trueValueType)
        {
            return new IfExpression(
                    new ComparisonExpression(operator, left, right),
                    result,
                    new Cast(new NullLiteral(), toSqlType(trueValueType)));
        }