Endpoint 'gRPC - Unimplemented service'

I have a service that is not behaving as it should. While troubleshooting it, I noticed this debug output:

Endpoint 'gRPC - Unimplemented service' with route pattern '{unimplementedService}/{unimplementedMethod}' is valid for the request path ... (the path of the non-working service).

What does this mean? I register my Grpc-service using `endpoints.MapGrpcService();`

The actual issue I was troubleshooting is that the Grpc-service is invoked, does it's work correctly and returns a class with two string properties. However, on the wire the response is empty (so the client gets a serialization error):

```
HTTP/1.1 200 OK
Content-Length: 0
Content-Type: application/grpc-web
Date: Fri, 08 Apr 2022 09:23:39 GMT
Server: Kestrel
Request-Context: appId=cid-v1:87cb2164-3464-497d-a7b4-80e9471bf6c3
Grpc-Status: 0
X-Content-Type-Options: nosniff
Strict-Transport-Security: max-age=31536000
```