How to handle missing relation inside withObservables

[maXXCZ1]

Hello, i would like to ask for a solution to fairly common problem tied to withObservables.

official documentation states this:

Reactive optional relations
Continuing the above example, if the comment has no author, the comment.author_id must be null. If comment.author_id has a value, the author record it refers to must be stored in the database, otherwise withObservables will throw an error that the record was not found.

My issue is, that i would like to handle case, when i have relation on model and i want observe it in withObservables.
But what if relatedModel does not exist? Or what if even myModel does not exist.

withObservables(["myModel"], ({myModel} : {myModel: MyModel})=> {

return {
my_relation_model: myModel?.relatedModel
}
})

i tried simple myModel?.relatedModel || of(null) which should also be the result i am looking for pretty much (or even better would be "simple" null)

I am fairly unfamiliar with Rxjs, but i tried to solve this in quite a few different ways, but none was successful.
I always end up with error relatedModel#1 not found which means complete crash of app.

Tried using defer, map, switchMap, pipe, nothing was working for me. Is there any way to handle this?

I know i can solve this by using query(), but i believe there should be more elegant solution for this which i struggle to find.