group by 1 isn't working in new engine

[rupal-bq]

Query:

 SELECT DATE_ADD(`calcs`.`date2`, INTERVAL 1 MONTH) AS `TEMP(Test)(2799254343)(0)` FROM `calcs` GROUP BY 1 

Error:

{
    "error": {
        "type": "IllegalStateException",
        "reason": "Unsupported type DATETIME to construct expression value from object for field: DATE_ADD(calcs.date2, Interval(value=1, unit=MONTH)), value: 1972-08-12.",
        "details": "Unsupported type DATETIME to construct expression value from object for field: DATE_ADD(calcs.date2, Interval(value=1, unit=MONTH)), value: 1972-08-12."
    },
    "status": 503
}

Was able to get a successful response after removing group by 1 from the query.