[GraphQL] Exception thrown when child nodes do not contain non-nullable fields

[bwegrzyn]

Not sure how else to name this issue, but I'm having a bizarre issue.

I have a recursive relationship of User->ReferredBy (also a User). When I issue a request to retrieve Users, I ask for most of the data on the main user, but keep the data I request on the ReferredBy relationship to a minimum. But if I don't request non-nullable fields on the ReferredBy relationship, the response ends up being an HTTP 400 with errors attached.

In the example below, one of the non-nullable fields on my User entity is points. It always an int and has a value of >= 0. If I do not request points on the ReferredBy relation, then an exception is thrown. However, I can skip points on the top level User without any issues.

This is the request I am issuing:

query GetUsers($cursor: String, $query: String) {
  users(after: $cursor, order: {name: "ASC"}, query: $query) {
    edges {
      cursor
      node {
        ...UserFields
      }
    }
    pageInfo {
      endCursor
      hasNextPage
    }
  }
}

fragment UserFields on User {
  id
  referredBy {
    id
    name
    email
    referralToken
  }
  name
  email
  referralToken
  points
}

This results in an exception being thrown with the following response:

{
  "errors": [
    {
      "debugMessage": "Cannot return null for non-nullable field User.points.",
      "message": "Internal server error",
      "category": "internal",
      "locations": [
        {
          "line": 29,
          "column": 3
        }
      ],
      "path": [
        "users",
        "edges",
        2,
        "node",
        "points"
      ]
    }
  ],
  "data": {
    "users": {
      "edges": [
        {
          "cursor": "MA==",
          "node": {
            "id": "/users/84cc1b30-6875-11e8-8dd5-f393655f85db",
            "referredBy": null,
            "name": "Administrator",
            "email": "admin@test.com",
            "referralToken": "623C33",
            "points": 50
          }
        },
        {
          "cursor": "MQ==",
          "node": {
            "id": "/users/3d2f955c-8005-11e8-925e-ffad03401b2c",
            "referredBy": {
              "id": "/users/65dc3b1e-69de-11e8-8be9-5beebe7a0b50",
              "name": "Test User 1",
              "email": "test1@test.com",
              "referralToken": "058D51"
            },
            "name": "Test User 2",
            "email": "test2@test.com",
            "referralToken": "A4965A",
            "points": 50
          }
        },
        {
          "cursor": "Mg==",
          "node": null
        }
      ],
      "pageInfo": {
        "endCursor": "Mg==",
        "hasNextPage": false
      }
    }
  }

The only way I can get rid of this error is to request all non-nullable fields on the ReferredBy User relation. The weird part is that I can completely skip these non-nullable fields on the top level User, but I must always request them on child User nodes.

[alanpoulain]

Strange behavior indeed. I think it's only the case when it's a recursive relationship since this scenario is working (RelatedDummy has non-nullable fields like symfony):

core/features/graphql/query.feature

Lines 60 to 86 in 797cea6

	Scenario: Retrieve an item through a GraphQL query with variables
	When I have the following GraphQL request:
	"""
	query DummyWithId($itemId: ID = "/dummies/1") {
	dummyItem: dummy(id: $itemId) {
	id
	name
	relatedDummy {
	id
	name
	}
	}
	}
	"""
	And I send the GraphQL request with variables:
	"""
	{
	"itemId": "/dummies/2"
	}
	"""
	Then the response status code should be 200
	And the response should be in JSON
	And the header "Content-Type" should be equal to "application/json"
	And the JSON node "data.dummyItem.id" should be equal to "/dummies/2"
	And the JSON node "data.dummyItem.name" should be equal to "Dummy #2"
	And the JSON node "data.dummyItem.relatedDummy.id" should be equal to "/related_dummies/2"
	And the JSON node "data.dummyItem.relatedDummy.name" should be equal to "RelatedDummy #2"

It needs some time to investigate. It may be a bug related to graphql-php.