Provide proper path in GraqhQL errors

[stuebingerb]

From https://spec.graphql.org/September2025/#sec-Errors.Error-Result-Format:

If an error can be associated to a particular field in the GraphQL result, it must contain an entry with the key "path" with a response path which describes the response position which raised the error. This allows clients to identify whether a null resolved result is a true value or the result of an execution error.

Example:

{
  hero(episode: $episode) {
    name
    heroFriends: friends {
      id
      name
    }
  }
}

Response:

{
  "errors": [
    {
      "message": "Name for character with ID 1002 could not be fetched.",
      "locations": [{ "line": 6, "column": 7 }],
      "path": ["hero", "heroFriends", 1, "name"]
    }
  ],
  "data": {
    "hero": {
      "name": "R2-D2",
      "heroFriends": [
        {
          "id": "1000",
          "name": "Luke Skywalker"
        },
        {
          "id": "1002",
          "name": null
        },
        {
          "id": "1003",
          "name": "Leia Organa"
        }
      ]
    }
  }
}

If the field which experienced an error was declared as Non-Null, the null result will bubble up to the next nullable field. In that case, the path for the error should include the full path to the result field where the error was raised, even if that field is not present in the response.

So if the name field above had a Non-Null return type, the resulting data would be different but the path must be the same:

{
  "errors": [
    {
      "message": "Name for character with ID 1002 could not be fetched.",
      "locations": [{ "line": 6, "column": 7 }],
      "path": ["hero", "heroFriends", 1, "name"]
    }
  ],
  "data": {
    "hero": {
      "name": "R2-D2",
      "heroFriends": [
        {
          "id": "1000",
          "name": "Luke Skywalker"
        },
        null,
        {
          "id": "1003",
          "name": "Leia Organa"
        }
      ]
    }
  }
}