Added debug message is runtime set does not exist

Scripts/Damageable.cs

@@ -1,4 +1,5 @@
 using UnityEngine;
+using UnityEngine.Events;
 
 namespace GameDev.CoreSystems
 {
@@ -14,6 +15,8 @@ namespace GameDev.CoreSystems
         [field: Header("Modifiers")]
         [field: SerializeField] public bool IsInvulnerable { get; private set; }
 
+        public UnityEvent DeathEvent;
+
         private void OnEnable()
         {
             _activeDamageableRuntimeSet.Add(this);
@@ -35,6 +38,7 @@ namespace GameDev.CoreSystems
             if (CurrentHealth >= 0) return;
 
             print($"{transform.parent.parent.name} died");
+            DeathEvent.Invoke();
         }
 
         #endregion

Scripts/Targetable.cs

@@ -19,7 +19,14 @@ namespace GameDev.CoreSystems
 
         private void OnEnable()
         {
-            _activeTargetableRuntimeSet.Add(this);
+            if (_activeTargetableRuntimeSet != null)
+            {
+                _activeTargetableRuntimeSet.Add(this);
+            }
+            else
+            {
+                Debug.LogError("TargetableRuntimeSet does not exist");
+            }
         }
 
         private void OnDisable()