Hello,
since the last update from Nest 7 to Nest 8 also RXJS got updated to > 7.4.0.
The call signature of Microservices has changed from .toPromise to lastValueFrom(...).
This change opened a possible bug if null is returned, which should be allowed in my opinion

The underlying node-cache-manger also discussed about allowing null values and allowed here in this really old post : Issue
Thanks for your opinion in advance :)
Best regards Meywether