Fix WifiCallingSettingsForSubTest

Bug: 378832412
Test: atest
Flag: EXEMPT fix test
Change-Id: Id45f472e87371eb00ba3412a39ccda5af5723e4b

tests/robotests/src/com/android/settings/wifi/calling/WifiCallingSettingsForSubTest.java

@@ -49,6 +49,7 @@ import android.telephony.ims.ImsMmTelManager;
 import android.view.View;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.lifecycle.LifecycleOwner;
 import androidx.preference.Preference;
 import androidx.preference.PreferenceScreen;
@@ -400,6 +401,11 @@ public class WifiCallingSettingsForSubTest {
             return null;
         }
 
+        @Override
+        public @Nullable String getPreferenceScreenBindingKey(@NonNull Context context) {
+            return null;
+        }
+
         @Override
         protected Object getSystemService(final String name) {
             switch (name) {