Auto-generated mutation payload incorrectly set to null when mutation returns null

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

We use .AddMutationConventions(applyToAllMutations: true) to automatically apply conventions to all our mutations. However, when null is returned from the mutation, it seems to return null for the entire auto-generated __payload type.

For example:

// mutation code
public async Task<GuardianProfile> DeleteProfileAndRelationships

// generated schema
deleteProfileAndRelationships: DeleteProfileAndRelationshipsPayload!

// error when DeleteProfileAndRelationships returns null GuardianProfile
{
  "errors": [
    {
      "message": "Cannot return null for non-nullable field.",
      "locations": [
        {
          "line": 4,
          "column": 3
        }
      ],
      "path": [
        "deleteProfileAndRelationships"
      ],
      "extensions": {
        "code": "HC0018"
      }
    }
  ]
}

Expected: Valid DeleteProfileAndRelationshipsPayload returned with a guardianProfile: null field

Actual: Nullability error thrown

Steps to reproduce

1. Use .AddMutationConventions(applyToAllMutations: true)
2. Create a simple mutation that returns a reference type
3. Observe that a non-nullable ___payload type is auto-generated in the schema
4. Return null from mutation
5. Observe that a nullability error is thrown
6. Now, use [UseMutationConvention(Disable = true)] to NOT use mutation convention
7. Observe that a nullable return type is specified in the schema, as expected
8. Return null from mutation
9. Observe that it works as expected, null is returned

Relevant log output

No response

Additional Context?

No response

Product

Hot Chocolate

Version

12.7.0

[nancyl-ol]

But why does it work without convention. It should also fail

GuardianProfile is a nullable type since it’s a reference type and we don’t have nullable reference types enabled (https://chillicream.com/docs/hotchocolate/v12/defining-a-schema/non-null#implicit-nullability). So without the convention, the mutation is allowed to return null.

With the convention enabled, the auto-generated mutation return type DeleteProfileAndRelationshipsPayload is non-nullable, which makes sense. However, when the mutation returns a null GuardianProfile, I am expecting

{
  "data": {
    "deleteProfileAndRelationships": {
      "guardianProfile": null
    }
  }
}

Instead, I think it is returning null for the entire DeleteProfileAndRelationships**Payload**, which causes the nullability error.

Can you create a minimal Repro?

Sure, working on creating one

[michaelstaib]

@nancyl-ol tanks for the repro. The issue here seems to be that this mutation has now input. Its a bug … By trying to repro your issue I found another related bug. I will fix both with 12.16.0

I will add some test cases first and you can expect a fix by the end of the week.