Unexpected execution error using Fusion and interface types

[maartenkools]

Product

Hot Chocolate

Version

13.9.11

Link to minimal reproduction

https://github.com/maartenkools/fusion-bug

Steps to reproduce

Using Fusion, make sure one of the sub graphs implements multiple types based on an interface. When you query those types, and include fields that come from different sub graphs, an error is generated: Unexpected Execution Error. This happens since 13.9.8, while on 13.9.7 it still works.

Also see the projected I've included in the report. It can be tested with the following query:

query Programmes {
    programmes {
        department {
            name
            displayName
        }
        id
        ... on AdministrativeProgramme {
            id
            departmentId
        }
        ... on DegreeProgramme {
            id
            departmentId
        }
    }
}

What is expected?

A result is returned

What is actually happening?

No result is returned, causing an error

Relevant log output

{
    "errors": [
        {
            "message": "Unexpected Execution Error",
            "extensions": {
                "message": "A GraphQL result must have data, errors or both.",
                "stackTrace": "   at HotChocolate.Execution.Processing.ResultBuilder.BuildResult()\r\n   at HotChocolate.Fusion.Execution.Nodes.QueryPlan.ExecuteAsync(FusionExecutionContext context, CancellationToken cancellationToken)\r\n   at HotChocolate.Fusion.Execution.FederatedQueryExecutor.ExecuteAsync(FusionExecutionContext context, CancellationToken cancellationToken)\r\n   at HotChocolate.Fusion.Execution.Pipeline.DistributedOperationExecutionMiddleware.InvokeAsync(IRequestContext context, IBatchDispatcher batchDispatcher)\r\n   at HotChocolate.Execution.Pipeline.OperationVariableCoercionMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.OperationResolverMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.OperationComplexityMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.OperationCacheMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.DocumentValidationMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.DocumentParserMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.DocumentCacheMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.TimeoutMiddleware.InvokeAsync(IRequestContext context)\r\n   at HotChocolate.Execution.Pipeline.ExceptionMiddleware.InvokeAsync(IRequestContext context)"
            }
        }
    ]
}

Additional context

No response

[maartenkools]

I've tested this with HC 14.rc0, and while it no longer produces an unexpected execution error, I do get a different error now:

{
    "errors": [
        {
            "message": "Cannot return null for non-nullable field.",
            "locations": [
                {
                    "line": 5,
                    "column": 13
                }
            ],
            "path": [
                "programmes",
                2,
                "department",
                "displayName"
            ],
            "extensions": {
                "code": "HC0018"
            }
        },
        {
            "message": "Cannot return null for non-nullable field.",
            "locations": [
                {
                    "line": 5,
                    "column": 13
                }
            ],
            "path": [
                "programmes",
                1,
                "department",
                "displayName"
            ],
            "extensions": {
                "code": "HC0018"
            }
        },
        {
            "message": "Cannot return null for non-nullable field.",
            "locations": [
                {
                    "line": 5,
                    "column": 13
                }
            ],
            "path": [
                "programmes",
                0,
                "department",
                "displayName"
            ],
            "extensions": {
                "code": "HC0018"
            }
        }
    ],
    "data": null
}