fixed nullable object warning

src-csharp/GameObject.cs

@@ -65,7 +65,8 @@ public class GameObject
         if(Components.ContainsKey(t))
             return false;
         
-        Component component = (Component)Activator.CreateInstance(t, this);
+        Component component = (Component?)Activator.CreateInstance(t, this) 
+            ?? throw new Exception($"can't create instance of class {t.FullName}");
         Components.Add(t, component);
         return true;
     }