Angular 5 Http Interceptors error when injecting service

Question

I am receiving the following strange dependency injection behavior when using custom HttpInterceptors in angular 5+.

The following simplified code works fine:

Answer 1

If in case, service class is declared in the same file of Injector class then service class should be declared and defined first. Followed by the Injector class where the service class injected as a dependency.

Following above structure does resolves the problem in my case.