N1QL: Merge query giving Invalid merge key msg on missing keys and keys with null values

1.Add `beer-sample` as a sample bucket.
2.Create a new bucket default.
3.Execute the following query:
merge into default using `beer-sample` on key `beer-sample`.`state` when matched then update set default.name="abc",default.age=21;
OR
merge into default using `beer-sample` on key to_string(`beer-sample`.`state`) when matched then update set default.name="abc",default.age=21;

Result:
{
"requestID": "88d4b52c-ace4-43c1-9eb4-e19b93a9cc7f",
"signature": null,
"results": [
],
"errors": [

{ "code": 5030, "msg": "Invalid MERGE key \u003cnil\u003e of type \u003cnil\u003e." }

],
"status": "errors",
"metrics":

{ "elapsedTime": "16.548202ms", "executionTime": "16.390232ms", "resultCount": 0, "resultSize": 0, "errorCount": 1 }

}

We get this error because some documents in beer-sample have value of state key as null or do not have state key.
It should ideally skip those docs.
Tried another test case with merge on missing/null value key and I get the same error message.
This query works fine if merge key has empty/not matching values.