Component used: AppCompat Version used: appcompat-1.2.0 Devices/Android versions reproduced on: Oreo, API level 26 & 27

To reproduce:

Create AppCompatTextView and invoke setCustomSelectionActionModeCallback(null).
Long click on its text to bring up the selection action menu.
Observe crash.

This arises from the fact that AppCompatTextView.setCustomActionModeCallback accepts nullables, but internally calls to TextViewCompat.wrapCustomSelectionActionModeCallback, which requires a non-null callback.

Offending lines:

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:appcompat/appcompat/src/main/java/androidx/appcompat/widget/AppCompatTextView.java;l=446

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:core/core/src/main/java/androidx/core/widget/TextViewCompat.java;l=516

To fix this, the OreoCallback wrapping should be skipped if the callback is null.