Union gives internal error, how should I query?

[factormaarten]

Hello,

I'm trying to create a union with the following definition:

union EventTypes = UserEvent | TradeEvent

type Event {
    type: String
    payload: EventTypes
}

type UserEvent {
    user: User
}

type TradeEvent {
    trade: Trade
}

When I query:

subscription events {
  events {
    type
    payload {
      ... on UserEvent {
      	user {
          id
        }
      }
    }
  }
}

The event message is simply passed along:

        return [
            'events' => function ($message) {
                return $message;
            }
        ];

The current return json is:

array(2) {
  ["type"]=>
  string(11) "UserCreated"
  ["payload"]=>
  array(1) {
    ["userEvent"]=>
    array(1) {
      ["user"]=>
      array(4) {
        ["id"]=>
        string(36) "03e87a02-bd3f-4cba-b6b7-36074389e777"
        ["firstName"]=>
        string(3) "Ted"
        ["lastName"]=>
        string(5) "Mosby"
        ["email"]=>
        string(13) "[email protected]"
      }
    }
  }
}

However the error I'm getting is:

{
  "errors": [
    {
      "message": "Internal server error",
      "extensions": {
        "category": "internal"
      },
      "locations": [
        {
          "line": 4,
          "column": 5
        }
      ],
      "path": [
        "events",
        "payload"
      ]
    }
  ],
  "data": {
    "events": {
      "type": "UserCreated",
      "payload": null
    }
  }
}

What am I doing wrong? It somehow doesn't seem to determine what kind of event it is.

[spawnia]

Consider https://webonyx.github.io/graphql-php/type-definitions/unions/ and https://webonyx.github.io/graphql-php/error-handling/#debugging-tools