Crash when the message doesn't have an imageUrl

I completed both tutorials for the FriendlyChat (Android/iOS swift), when you add pictures in your swift application, if you are using the same database the android app will crash trying to load the messages because in the swift app "imageUrl" is stored as "imageURL" and "photoUrl" is "photoURL" so the app crashes at

`if (imageUrl.startsWith("gs://")) {` (line 229 I believe)

because imageUrl is actually stored as imageURL.