message: Check null on onboarding callback (lib)
diff: @@ -815,7 +815,9 @@ void GUI::DisplayIdleNotification(const std::string &guid,
  }
  void GUI::DisplayOnboarding(const OnboardingType onboarding_type) {
  + if (on_display_onboarding_) {
  on_display_onboarding_(onboarding_type);
  }
  +}
  } // namespace toggl
  