When is a logger a dependency?

There are some discussion about whether loggers should get injected into your classes (dependency injection) or if you should use the logger facade (like LogManager.GetLogger<MyClass>()).

The answer rather simple:

As for all classes, dependencies which is mandatory should get injected.

That means that you should inject the logger if the class will fail without it (= not deliver the expected result). If the class can work without a logger: simply use the logger facade.