Fixed: Unhandled Exception: Java.Lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.ContentFrameLayout.setId(int)' on a null object reference occurred - Luke Alderton
Fix "java.lang.NullPointerException" in Android Studio - GeeksforGeeks
java.lang.NullPointerException: Attempt to invoke virtual method android studio - Stack Overflow