fix: add null check (#467)

UOP1_Project/Assets/Scripts/Events/ScriptableObjects/IntEventChannelSO.cs

-using UnityEngine.Events;
-using UnityEngine;
+using UnityEngine;
+using UnityEngine.Events;
 
 /// <summary>
 /// This class is used for Events that have one int argument.
 	public UnityAction<int> OnEventRaised;
 	public void RaiseEvent(int value)
 	{
-		OnEventRaised.Invoke(value);
+		if (OnEventRaised != null)
+			OnEventRaised.Invoke(value);
 	}
 }