No instruction on `private fun signIn` in SignInActivity.kt

In the `SignInActivity.kt` file there is a `private fun signIn()` function between the `onStart` function and the `onSignInResult` function that has a TODO that reads `// TODO: implement`:

`private fun signIn() {
// TODO: implement
}`

I see no instruction for this line of code and I am unable to create an account in the app. I'm assuming this has something to do with it. This function is also missing from the `build-android` finished project.