Refreshing Bluetooth devices will clear all available devices.

Bug: 16851309
Change-Id: I9ffb1ddaeb8e785be145ea79467fc361a022d8d7

src/com/android/settings/bluetooth/DeviceListPreferenceFragment.java

@@ -167,6 +167,12 @@ public abstract class DeviceListPreferenceFragment extends
      }
 
     void createDevicePreference(CachedBluetoothDevice cachedDevice) {
+        if (mDeviceListGroup == null) {
+            Log.w(TAG, "Trying to create a device preference before the list group/category "
+                    + "exists!");
+            return;
+        }
+
         BluetoothDevicePreference preference = new BluetoothDevicePreference(
                 getActivity(), cachedDevice);