Converts Most Destroys to use QDEL_NULL

code/modules/modular_computers/computers/machinery/modular_computer.dm

@@ -41,9 +41,7 @@ var/list/global_modular_computers = list()
 	global_modular_computers.Add(src)
 
 /obj/machinery/modular_computer/Destroy()
-	if(cpu)
-		qdel(cpu)
-		cpu = null
+	QDEL_NULL(cpu)
 	return ..()
 
 /obj/machinery/modular_computer/attack_ghost(mob/dead/observer/user)

code/modules/modular_computers/file_system/programs/engineering/alarm.dm

@@ -18,8 +18,7 @@
 /datum/computer_file/program/alarm_monitor/Destroy()
 	for(var/datum/alarm_handler/AH in alarm_handlers)
 		AH.unregister(src)
-	qdel(alarm_handlers)
-	alarm_handlers = null
+	QDEL_NULL(alarm_handlers)
 	return ..()
 
 /datum/computer_file/program/alarm_monitor/proc/update_icon()

code/modules/modular_computers/hardware/ai_slot.dm

@@ -11,9 +11,7 @@
 	var/locked = FALSE
 
 /obj/item/weapon/computer_hardware/ai_slot/Destroy()
-	if(stored_card)
-		qdel(stored_card)
-		stored_card = null
+	QDEL_NULL(stored_card)
 	return ..()
 
 

code/modules/modular_computers/hardware/battery_module.dm

@@ -14,9 +14,7 @@
 	..()
 
 /obj/item/weapon/computer_hardware/battery/Destroy()
-	if(battery)
-		qdel(battery)
-		battery = null
+	QDEL_NULL(battery)
 	return ..()
 
 /obj/item/weapon/computer_hardware/battery/on_remove(obj/item/device/modular_computer/M, mob/living/user = null)

code/modules/modular_computers/hardware/card_slot.dm

@@ -11,12 +11,8 @@
 	var/obj/item/weapon/card/id/stored_card2 = null
 
 /obj/item/weapon/computer_hardware/card_slot/Destroy()
-	if(stored_card)
-		qdel(stored_card)
-		stored_card = null
-	if(stored_card2)
-		qdel(stored_card2)
-		stored_card2 = null
+	QDEL_NULL(stored_card)
+	QDEL_NULL(stored_card2)
 	return ..()
 
 /obj/item/weapon/computer_hardware/card_slot/GetAccess()