Issues with group by in sql

I am trying to use sql-jdbc driver with tableau and hit a road block. Falling back to curl, i am seeing same issue with group by queries using 1.6.0 versions of elastic search and sql-jdbc driver
Here is my query to get all the records in table

curl -X POST "localhost:9200/_opendistro/_sql?format=csv" -H 'Content-Type: application/json' -d'
{
  "query": "select * from employees"
}
' -u admin:admin
 user_name,name, phone, age
 vkoya,Venkata Koya, 937-839-1121, 13
 tkoya,Tejasvi Koya, 112-121-1244, 11
 tkoya,Tanmayi Koya, 992-122-1212, 1
 v_koya,Venkatakoya, 932-1111231, 12

Now doing a group by

curl -X POST "localhost:9200/_opendistro/_sql?" -H 'Content-Type: application/json' -d'
{
  "query": "select name from employees GROUP BY name.keyword"
}
' -u admin:admin
{
  "error": {
    "reason": "There was internal problem at backend",
    "details": "invalid value operation on MISSING_VALUE",
    "type": "IllegalStateException"
  },
  "status": 500
}

Hi @venkatakoya, there is an open issue for this: https://github.com/opendistro-for-elasticsearch/sql/issues/401.