--- a/dom/media/MediaStreamGraph.cpp
+++ b/dom/media/MediaStreamGraph.cpp
@@ -971,16 +971,19 @@ MediaStreamGraphImpl::NotifyInputData(co
   {
     MonitorAutoLock lock(mMonitor);
     // Either we have an audio input device, or we just removed the audio input
     // this iteration, and we're switching back to an output-only driver next
     // iteration.
     MOZ_ASSERT(mInputDeviceID || CurrentDriver()->Switching());
   }
 #endif
+  if (!mInputDeviceID) {
+    return;
+  }
   nsTArray<RefPtr<AudioDataListener>>* listeners = mInputDeviceUsers.GetValue(mInputDeviceID);
   MOZ_ASSERT(listeners);
   for (auto& listener : *listeners) {
     listener->NotifyInputData(this, aBuffer, aFrames, aRate, aChannels);
   }
 }
 
 void MediaStreamGraphImpl::DeviceChangedImpl()