[le audio] Null check when setting le audio active device

Bug: 381557098
Flag: EXEMPT, null check
Test: atest ActiveDeviceManagerTest
Change-Id: Ic0a8eab6d3e8a7369689fb063a75c38349b3de0e
diff --git a/android/app/src/com/android/bluetooth/btservice/ActiveDeviceManager.java b/android/app/src/com/android/bluetooth/btservice/ActiveDeviceManager.java
index 9d744db..c738e3d 100644
--- a/android/app/src/com/android/bluetooth/btservice/ActiveDeviceManager.java
+++ b/android/app/src/com/android/bluetooth/btservice/ActiveDeviceManager.java
@@ -412,7 +412,7 @@
                 final LeAudioService leAudioService = mFactory.getLeAudioService();
                 setA2dpActiveDevice(null, true);
                 setHfpActiveDevice(null);
-                if (Flags.admVerifyActiveFallbackDevice()) {
+                if (Flags.admVerifyActiveFallbackDevice() && leAudioService != null) {
                     setLeAudioActiveDevice(
                             null, !leAudioService.getActiveDevices().contains(device));
                 } else {