[Transform] cannot group by boolean

[hendrikmuhs]

Reported via discuss:

Grouping boolean using a terms aggregation throws in transform:

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Value of type [class java.lang.Boolean] is not supported"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "Value of type [class java.lang.Boolean] is not supported"
  },
  "status" : 400
}

The above is possible with aggs and composite aggs. The error message originates from IDGenerator which does not know how to treat a boolean.

[elasticmachine]

Pinging @elastic/ml-core (:ml/Transform)