Add null check in displayPreference

Change-Id: I3afaa3f587dc5c9989d5e520f1c8a0b33e57ec7d
Fixes: 109740402
Test: ZenModeStarredContactsPreferenceControllerTest.java

src/com/android/settings/notification/ZenModeStarredContactsPreferenceController.java

@@ -68,8 +68,11 @@ public class ZenModeStarredContactsPreferenceController extends
     public void displayPreference(PreferenceScreen screen) {
         super.displayPreference(screen);
         mPreference = screen.findPreference(KEY);
+
+        if (mPreference != null) {
             mPreference.setOnPreferenceClickListener(this);
         }
+    }
 
     @Override
     public String getPreferenceKey() {

tests/robotests/src/com/android/settings/notification/ZenModeStarredContactsPreferenceControllerTest.java

@@ -190,4 +190,13 @@ public class ZenModeStarredContactsPreferenceControllerTest {
             assertThat(contacts.get(i)).isNotNull();
         }
     }
+
+    @Test
+    public void nullPreference_displayPreference() {
+        when(mPreferenceScreen.findPreference(mMessagesController.getPreferenceKey()))
+                .thenReturn(null);
+
+        // should not throw a null pointer
+        mMessagesController.displayPreference(mPreferenceScreen);
+    }
 }