Add @Nullable to CompoundButton#setOnCheckedChangeListener().

Test: n/a

Change-Id: I3db93bfcfba528e7271be21356e585e9f9a0799d

core/java/android/widget/CompoundButton.java

@@ -169,7 +169,7 @@ public abstract class CompoundButton extends Button implements Checkable {
      *
      * @param listener the callback to call on checked state change
      */
-    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
+    public void setOnCheckedChangeListener(@Nullable OnCheckedChangeListener listener) {
         mOnCheckedChangeListener = listener;
     }