https://developer.android.com/jetpack/androidx/releases/lifecycle#2.4.0-alpha03

API Changes

Source-breaking change: ViewModelProvider has been rewritten in Kotlin. ViewModelProvider.Factory.create method now longer allows nullable generic. (I9b9f6)

Basically, this:

override fun <T : ViewModel?> create(modelClass: Class<T>): T

becomes this:

override fun <T : ViewModel> create(modelClass: Class<T>): T

Since the old nullability was just automatically added by the IDE and not actually enforced by the compiler, a new version which is non-nullable is still binary-compatible with projects using lifecycle-viewmodel:2.3.1 or earlier.