Add @Nullable to CompoundButton#setOnCheckedChangeListener().

Test: n/a

Change-Id: I3db93bfcfba528e7271be21356e585e9f9a0799d
diff --git a/core/java/android/widget/CompoundButton.java b/core/java/android/widget/CompoundButton.java
index dd63fef..3213a34 100644
--- a/core/java/android/widget/CompoundButton.java
+++ b/core/java/android/widget/CompoundButton.java
@@ -169,7 +169,7 @@
      *
      * @param listener the callback to call on checked state change
      */
-    public void setOnCheckedChangeListener(OnCheckedChangeListener listener) {
+    public void setOnCheckedChangeListener(@Nullable OnCheckedChangeListener listener) {
         mOnCheckedChangeListener = listener;
     }