Bugfix: Prevent NPE if damage stack is empty when something dies

Author: hydrozoa-yt

src/main/kotlin/api/api/combat/death/DeathHookHandler.kt

@@ -104,7 +104,7 @@ object DeathHookHandler {
      * @param source The [Mob] responsible for the kill.
      * @param stage The current [DeathStage] of the death sequence.
      */
-    fun onDeath(victim: Mob, source: Mob, stage: DeathStage) {
+    fun onDeath(victim: Mob, source: Mob?, stage: DeathStage) {
         if (victim is Npc) {
             val receiver = DeathHookReceiver(victim, source, stage)
             val lookup = npcHooks[victim.id]

src/main/kotlin/api/api/combat/death/dsl/DeathHookReceiver.kt

@@ -41,7 +41,7 @@ import io.luna.game.model.mob.MobDeathTask.DeathStage
  * @property source The entity responsible for causing the death.
  * @property stage The current death stage ([DeathStage.PRE_DEATH], [DeathStage.DEATH], [DeathStage.POST_DEATH]).
  */
-class DeathHookReceiver<T : Mob>(val victim: T, val source: Mob, private val stage: DeathStage) {
+class DeathHookReceiver<T : Mob>(val victim: T, val source: Mob?, private val stage: DeathStage) {
 
     /**
      * Executes logic during the pre-death stage. This block runs before the entity officially dies.