Gracefully handle backend failures in Expo app

App.js

@@ -102,6 +102,7 @@ const MainNavigation = ({ route }) => {
         registerForPushNotificationsAsync().then(async (token) => {
             let isLoggedIn = await API.isLoggedIn();
             if (!isLoggedIn) return false;
+            if (!token) return false;
             API.registerToken(token);
             return setExpoPushToken(token);
         });