android studio errors about ‘android.annotation.NonNull’ in handler.java

I am using Android Studio Arctic Fox(2020.3.1).
I’ve been having some trouble with handler.java
Most of the errors are

‘android.annotation.NonNull’ is not public in ‘android.annotation’. Cannot be accessed from an outside package

I’ve tried to fix android with androidx. but I don’t know why this error occurs. please help me.

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Answer

that’s not important!

you will get these kinds of errors when navigating android source.

that won’t affect your android project and everything will be compiled successfully ✔