No implementation found for method isAvailable on channel dev.gilder.tom/apple_sign_in

I've been through your Udemy Flutter & Firebase course. I wanted to study this demo for additional insights. Thank you for making it available to all.

I'm seeing a hitch in iOS. The device screen (in my simulator) does not get past a blank white screen. There is no widget tree in the Flutter Inspector in IntelliJ and no error output. Running it in Xcode, this one bit of output seems especially suspicious.

```
Unhandled Exception: MissingPluginException
(No implementation found for method isAvailable on channel dev.gilder.tom/apple_sign_in)
```

There is a lot more to that output (I'll post here if you want to see it) but I thought I'd start by asking if this one line could point to the reason for the blank white screen?