chore: Finalize Don't Set Fields to Null Anymore

Engine.Core/GameManager.cs

@@ -2,6 +2,7 @@ using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Graphics;
 
 using Syntriax.Engine.Core.Abstract;
+using Syntriax.Engine.Core.Exceptions;
 using Syntriax.Engine.Core.Factory;
 
 namespace Syntriax.Engine.Core;
@@ -63,6 +64,8 @@ public class GameManager : IInitialize
         if (Initialized)
             return false;
 
+        NotAssignedException.Check(this, StateEnable);
+
         foreach (var gameObject in GameObjects)
             gameObject.Initialize();
 
@@ -84,7 +87,7 @@ public class GameManager : IInitialize
 
     public bool Assign(IStateEnable stateEnable)
     {
-        if (_stateEnable is not null)
+        if (Initialized)
             return false;
 
         _stateEnable = stateEnable;