Fixed abstract class NotificationDTO Generate Error

Map/NotificationServiceMap.cs

@@ -152,6 +152,10 @@ namespace FlutterCodeGenerator.Map
                         importServiceList.Add(importService);
                     }
                 }
+                if(notificationModelType.ParameterType.IsAbstract)
+                {
+                    continue;
+                }
                 var instance = Activator.CreateInstance(notificationModelType.ParameterType);
                 var instanceString = JsonSerializer.Serialize(instance);
                 try