make null checkability for variable

lib/providers/app_provider.dart

@@ -477,7 +477,7 @@ class AppProvider with ChangeNotifier {
       _pluginRunProgress = pluginItem?.get('progress') ?? 0;
       if (pluginItem != null) {
         _importerId = pluginItem.id;
-        ready = _pluginRunProgress! >= 1.0;
+        ready = (_pluginRunProgress ?? 0) >= 1.0;
       }
 
       AppLogger.debug('Plugin progress: $_pluginRunProgress');