How to use firebase query with a route resolver

Question

I'm implementing a route resolver but I'm having type issues and I'm not sure how to resolve.

I'm navigating to a Group page like a social media group and I want to resolve the Group Data before routing to the page so I'm using a resolver.

    resolve(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): Promise<IGroup> {
        const groupId = route.paramMap.get('id');
        const test = this.groupDataService.getMyGroup(groupId);
        return test;
    }

The problem is that my groupDateService is returning a document reference.

  getMyGroup(id) {
    const userGroup: firebase.firestore.DocumentReference = firebase.firestore().doc(`groups/${id}`);
    return  userGroup.get();
  }

I'm not sure how to make these types match. When the groupDataService returns the document I need it to be of type IGroup.

Any help would be greatly appreciated.