Fix build error due to null annotations in core platform API

Change https://r.android.com/1667508 adds nullability annotations to
the core platform APIs which broke this code with the error:

javadoc: error - In doclet class com.google.doclava.Doclava,  method
start has thrown an exception
java.lang.reflect.InvocationTargetException
com.sun.tools.javac.code.Symbol$CompletionFailure: class file for
androidx.annotation.RecentlyNonNull not found

Bug: 183938110
Bug: 185929373
Test: m checkbuild

Change-Id: I83e3071f851720a9f719cb226f0e84fd731a8f37
Merged-In: I83e3071f851720a9f719cb226f0e84fd731a8f37