Don't cast LegacyAdapter to NonLegacyAdapter

Bug: 20681571
Change-Id: I32a8e9df31eead4068ceb7c7c39b07f7144fee91
(cherry picked from commit e48aefc4022ceca71401d1490b595a8f71e95611)
diff --git a/src/com/android/contacts/list/LegacyPhoneNumberPickerFragment.java b/src/com/android/contacts/list/LegacyPhoneNumberPickerFragment.java
index b88fa71..d62c730 100644
--- a/src/com/android/contacts/list/LegacyPhoneNumberPickerFragment.java
+++ b/src/com/android/contacts/list/LegacyPhoneNumberPickerFragment.java
@@ -42,6 +42,12 @@
     }
 
     @Override
+    protected String getLookupKey(int position) {
+        // There is no lookup key for the legacy adapter.
+        return null;
+    }
+
+    @Override
     protected ContactEntryListAdapter createListAdapter() {
         LegacyPhoneNumberListAdapter adapter = new LegacyPhoneNumberListAdapter(getActivity());
         adapter.setDisplayPhotos(true);