Writing mutations with null values in relations

[joskfg]

Describe the bug

If you tries to execute a mutation with a null value in a relation, the mutation fails. It could be regression over #1021.

Expected behavior/Solution

The mutation should work without working with the relation

Steps to reproduce

This mutation variables will work:

{
  "book": { 
    "upsert": [
      {
       "title": "test",
        "chapter": {
         "upsert": [{ "something": "value"}]
       }
      }
     ]
  }
}

This mutation variables won't work:

{
  "book": { 
    "upsert": [
      {
       "title": "test",
        "chapter": null
      }
     ]
  }
}

This mutation variables will work:

{
  "book": { 
    "upsert": [
      {
       "title": "test",
      }
     ]
  }
}

Output/Logs

Click to expand

{"message":"Argument 1 passed to Nuwave\\Lighthouse\\Execution\\Arguments\\ArgPartitioner::nestedArgResolvers() must be an instance of Nuwave\\Lighthouse\\Execution\\Arguments\\ArgumentSet, null given, called in /opt/app/vendor/nuwave/lighthouse/src/Execution/Arguments/ResolveNested.php on line 33","context":{"exception":{"class":"TypeError","message":"Argument 1 passed to Nuwave\\Lighthouse\\Execution\\Arguments\\ArgPartitioner::nestedArgResolvers() must be an instance of Nuwave\\Lighthouse\\Execution\\Arguments\\ArgumentSet, null given, called in /opt/app/vendor/nuwave/lighthouse/src/Execution/Arguments/ResolveNested.php on line 33","code":0,"file":"/opt/app/vendor/nuwave/lighthouse/src/Execution/Arguments/ArgPartitioner.php:26"}},"level":400,"level_name":"ERROR","channel":"testing","datetime":"2020-06-17T12:29:48.107377+00:00","extra":{}}

Lighthouse Version

4.14.1