Angular / Ivy error : Error: Token InjectionToken XXXXXXXXX is missing a ɵprov definition

Question

Getting the error after updating to Angular 9 / Ivy compiler

ERROR Error: Token InjectionToken XXXXXXXXX is missing a ɵprov definition.
    at injectableDefOrInjectorDefFactory (vendor.js:47105)
    at providerToFactory (vendor.js:47210)
    at resolveProvider$1 (vendor.js:56430)

Answer 1

This can occur if you try to explicitly override an inherited injectable with undefined or null.

In Angular 8 this was ok

    {
        provide: AMBIENT_CART,
        useExisting: undefined
    }

With Angular 9 it needs to be changed to

    {
        provide: AMBIENT_CART,
        useValue: undefined
    }

If you're curious: In my case I was doing this for safety reasons, to make sure I didn't use this particular injectable by mistake.