Global context is null

Question

I'm using the global context as outlined in Get the Global Context in Flutter in a RetryPolicy which references an auth service when I get a 401:

class ExpiredTokenRetryPolicy extends RetryPolicy {
  @override
  int get maxRetryAttempts => 1;

  @override
  bool shouldAttemptRetryOnException(Exception reason) {
    return false;
  }

  @override
  Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async {
    if (response.statusCode == 401) {
      await Provider.of<UserProfileService>(NavigationService.navigatorKey.currentContext!, listen: false).initLogin();
      return true;
    }

    return false;
  }
}

Randomly the NavigationService.navigatorKey.currentContext is null, is there anyway I can reinitialise this?