Nullreference exeption in AddApplicationInsightsTelemetryWorkerService

Question

In a .dll I have a method to send an Azure Application Event. The method contains the following lines:

        TelemetryConfiguration configuration = new TelemetryConfiguration(orchestrationKeyToUse);
        IServiceCollection services = new ServiceCollection();

        services.AddSingleton<ITelemetryInitializer, KnaufCustomTelemetryInitializer>();
        services.AddApplicationInsightsTelemetryWorkerService(orchestrationKeyToUse);
        services.AddApplicationInsightsTelemetryProcessor<KnaufCustomTelemetryProcessor>();

When I call the method from an exe, there is no problem.
When I call the method in an interface method of an addin, it throws an Nullreference-Exception in AddApplicationInsightsTelemetryWorkerService.
I tried to start a thread and call the method in the thread, but it throws the Nullreference-Exception there, too.
What could be the reason?