Fix NPE in AudioSwitchPreferenceController

Change-Id: Ic97d1a6269a6d98ffd15a9b512f6ae24ff1c5b5e
Test: Unit Test to verify nullness
Bug: 338892614

tests/robotests/src/com/android/settings/sound/AudioOutputSwitchPreferenceControllerTest.java

@@ -516,6 +516,15 @@ public class AudioOutputSwitchPreferenceControllerTest {
         assertThat(mEmptyDevices).containsExactly(connectedBtLeAduioDevice1);
     }
 
+    @Test
+    public void getConnectedLeAudioDevices_nullConnectedDevices_returnEmptyList() {
+      when(mLeAudioProfile.getConnectedDevices()).thenReturn(null);
+
+      List<BluetoothDevice> connectedDevices = mController.getConnectedLeAudioDevices();
+
+      assertThat(connectedDevices.isEmpty()).isTrue();
+    }
+
     @Test
     public void findActiveLeAudioDevice_noActiveDevice_returnNull() {
         mLeAudioActiveDevices.clear();