Values selection does not gracefully deal with missing fields within an array objects.

[o0Ignition0o]

Steps to reproduce:

Run this query:

query {
  stuff {
    id
    aDetailsIsEnabled
  }
}

Against a router with the schema pasted below.

The router will send a first query to SUB1:

{ "query": "{stuff{__typename id details{enabled}}}" }

Provide a response that has null elements in the details list:

{
  "data": {
    "stuff": {
      "__typename": "Stuff",
      "id": 12345,
      "details": [ 
        {"enabled": true},
        null,
        {"enabled": false}
      ]
    }
  }
}

Check the second subgraph request being made:

Expected (which is done in the gateway):

{
  "query": "query($representations:[_Any!]!){_entities(representations:$representations){...on Stuff{aDetailsIsEnabled}}}",
  "variables": {
    "representations": [
      {
        "__typename": "Stuff",
        "id": 12345,
        "details": [
          {
            "enabled": true
          },
          null,
          {
            "enabled": false
          }
        ]
      }
    ]
  }
}

Actual (in the router):

{
  "query": "query($representations:[_Any!]!){_entities(representations:$representations){...on Stuff{aDetailsIsEnabled}}}",
  "variables": {
    "representations": [
      {
        "__typename": "Stuff",
        "id": 12345
      }
    ]
  }
}

Details is missing in the router's representations because we failed to find the "enabled" field while selecting the relevant values in the selection set within the null items. We should use Value::Null in the array's item and keep processing them.

Schema for reference:

schema
  @link(url: "https://specs.apollo.dev/link/v1.0")
  @link(url: "https://specs.apollo.dev/join/v0.3", for: EXECUTION)
{
  query: Query
}

directive @join__enumValue(graph: join__Graph!) repeatable on ENUM_VALUE

directive @join__field(graph: join__Graph, requires: join__FieldSet, provides: join__FieldSet, type: String, external: Boolean, override: String, usedOverridden: Boolean) repeatable on FIELD_DEFINITION | INPUT_FIELD_DEFINITION

directive @join__graph(name: String!, url: String!) on ENUM_VALUE

directive @join__implements(graph: join__Graph!, interface: String!) repeatable on OBJECT | INTERFACE

directive @join__type(graph: join__Graph!, key: join__FieldSet, extension: Boolean! = false, resolvable: Boolean! = true, isInterfaceObject: Boolean! = false) repeatable on OBJECT | INTERFACE | UNION | ENUM | INPUT_OBJECT | SCALAR

directive @join__unionMember(graph: join__Graph!, member: String!) repeatable on UNION

directive @link(url: String, as: String, for: link__Purpose, import: [link__Import]) repeatable on SCHEMA

type Details
  @join__type(graph: SUB1)
  @join__type(graph: SUB2)
{
  enabled: Boolean
}

scalar join__FieldSet

enum join__Graph {
  SUB1 @join__graph(name: "sub1", url: "http://localhost:4002/test")
  SUB2 @join__graph(name: "sub2", url: "http://localhost:4002/test2")
}

scalar link__Import

enum link__Purpose {
  """
  `SECURITY` features provide metadata necessary to securely resolve fields.
  """
  SECURITY

  """
  `EXECUTION` features provide metadata necessary for operation execution.
  """
  EXECUTION
}

type Query
  @join__type(graph: SUB1)
  @join__type(graph: SUB2)
{
  stuff: Stuff @join__field(graph: SUB1)
}

type Stuff
  @join__type(graph: SUB1, key: "id")
  @join__type(graph: SUB2, key: "id", extension: true)
{
  id: ID
  details: [Details] @join__field(graph: SUB1) @join__field(graph: SUB2, external: true)
  aDetailsIsEnabled: Boolean @join__field(graph: SUB2, requires: "details { enabled }")
}