conventions: Does "WithExposedExceptions" work as expected?

I have set:

engine.WithExposedExceptions(false);

but exceptions from resolvers (that are not ExecutionErrors) are still exposed. Specifically, a System.NotSupported exception is exposed as:

{
  "data": ...,
  "errors": [
    {
      "message": "Specified method is not supported.",
      "locations": [
        {
          "line": 3,
          "column": 5
        }
      ],
      "path": [...],
      "extensions": {
        "code": "NOT_SUPPORTED"
      }
    }
  ]
}

I’m returning the result via:

return enging.SerializeResult(result);

What am I missing? How can I prevent exceptions that are not ExecutionErrors from being exposed?