fix: Backport consistency and correctness fixes (7.x)

[dcodeIO]

Backports #2287, #2293 and #2275 to 7.x.

[UnderKoen]

Hi @dcodeIO , I think backporting #2287 is incorrect as failing for Message.fromObject(null) is a change in contract and should not happen in a minor version change.

This causes errors for us in nestjs where the null value cannot be converted into google.protobuf.Empty.

I feel like returning null or {} is approperiate especially for google.protobuf.Empty

[dcodeIO]

Did a quick check, and you are right that this used to work for fieldless messages. That behavior was accidental, though: null is not an empty message; {} is.

If needed, a narrow compatibility fix here could be to allow null precisely for fieldless messages, but I am not yet convinced that preserving this accidental behavior of accepting an invalid value is the right tradeoff? Turns out this is a relatively simple fix.

[UnderKoen]

For my use case it doesn't really matter what is return, just as long as it does not throw an error.

It may be that @grpc/proto-loader should handle the null case better.

We ran into this problem because of our nestjs implementation where we implement function which return google.protobuf.Empty as void an there for it returns undefined into the flow and throws :/