Fix notification channel creation

app/src/main/java/com/nextcloud/talk/jobs/NotificationWorker.java

@@ -304,7 +304,7 @@ public class NotificationWorker extends Worker {
                     groupName);
 
             if (decryptedPushMessage.getType().equals("chat")) {
-                NotificationUtils.createNotificationChannel(notificationManager,
+                NotificationUtils.createNotificationChannel(context,
                         NotificationUtils.NOTIFICATION_CHANNEL_MESSAGES_V3, context.getResources()
                                 .getString(R.string.nc_notification_channel_messages), context.getResources()
                                 .getString(R.string.nc_notification_channel_messages), true,
@@ -312,7 +312,7 @@ public class NotificationWorker extends Worker {
 
                 notificationBuilder.setChannelId(NotificationUtils.NOTIFICATION_CHANNEL_MESSAGES_V3);
             } else {
-                NotificationUtils.createNotificationChannel(notificationManager,
+                NotificationUtils.createNotificationChannel(context,
                         NotificationUtils.NOTIFICATION_CHANNEL_CALLS_V3, context.getResources()
                                 .getString(R.string.nc_notification_channel_calls), context.getResources()
                                 .getString(R.string.nc_notification_channel_calls_description), true,

app/src/main/java/com/nextcloud/talk/utils/NotificationUtils.java

@@ -44,11 +44,14 @@ public class NotificationUtils {
     public static final String NOTIFICATION_CHANNEL_CALLS_V3 = "NOTIFICATION_CHANNEL_CALLS_V3";
 
     @TargetApi(Build.VERSION_CODES.O)
-    public static void createNotificationChannel(NotificationManager notificationManager,
+    public static void createNotificationChannel(Context context,
                                                  String channelId, String channelName,
                                                  String channelDescription, boolean enableLights,
                                                  int importance) {
 
+        NotificationManager notificationManager =
+                (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
+
         if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O
                 && notificationManager.getNotificationChannel(channelId) == null) {