Add a null check for mImpl.

Bug: 30005941
Change-Id: I1212aa66be71b7ee0e990596272a33fa7530770f
diff --git a/services/voiceinteraction/java/com/android/server/voiceinteraction/VoiceInteractionManagerService.java b/services/voiceinteraction/java/com/android/server/voiceinteraction/VoiceInteractionManagerService.java
index 794a73e..6aa12de 100644
--- a/services/voiceinteraction/java/com/android/server/voiceinteraction/VoiceInteractionManagerService.java
+++ b/services/voiceinteraction/java/com/android/server/voiceinteraction/VoiceInteractionManagerService.java
@@ -1043,7 +1043,9 @@
         public void registerVoiceInteractionSessionListener(
                 IVoiceInteractionSessionListener listener) {
             enforceCallingPermission(Manifest.permission.ACCESS_VOICE_INTERACTION_SERVICE);
-            mImpl.registerVoiceInteractionSessionListener(listener);
+            if (mImpl != null) {
+                mImpl.registerVoiceInteractionSessionListener(listener);
+            }
         }
 
         @Override