Fix a crash

app/src/main/java/app/fedilab/android/mastodon/ui/drawer/NotificationAdapter.java

@@ -225,6 +225,9 @@ public class NotificationAdapter extends RecyclerView.Adapter<RecyclerView.ViewH
     @Override
     public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int position) {
         Notification notification = notificationList.get(position);
+        if (notification == null || notification.account == null) {
+            return;
+        }
         if (getItemViewType(position) == TYPE_FOLLOW || getItemViewType(position) == TYPE_FOLLOW_REQUEST || getItemViewType(position) == TYPE_ADMIN_REPORT || getItemViewType(position) == TYPE_ADMIN_SIGNUP) {
             ViewHolderFollow holderFollow = (ViewHolderFollow) viewHolder;
             SharedPreferences sharedpreferences = PreferenceManager.getDefaultSharedPreferences(context);