Conversation UI uses java.util.Objects, which requires API 19
ConversationActivity and ConversationViewModel use Objects.requireNonNull(), which was added in Java 7 and requires API 19 on Android.
Strangely, although the tooltip in Android Studio shows the API 19 requirement, the IDE and compiler don't complain about the missing method. The method works as expected: if null is passed, it throws a NullPointerException. But the stacktrace starts at the caller, not at Objects.requireNonNull().
It seems the method's being inlined at some point, perhaps by ProGuard or desugar. Setting
-dontoptimize in the ProGuard config, which should disable inlining, doesn't make a difference.
I think we should probably remove calls to this method, as we don't know where it's being inlined, and if it stopped being inlined in the future the app would fail to start on API < 19.