fallbackInitialize
Fallback initialization logic for the dependencies when Injector is not available. This could happen when the app process is killed and static Injectors are cleared up. An Injectable should check when this happens and call this function manually to recreate the Dagger dependency graph.
Return
The Injector created during fallback. It must be non-null when the Injectable class is responsible for injecting into other classes. Otherwise, the class might inject its own dependencies and return null.