Converts Most Destroys to use QDEL_NULL

code/modules/assembly/igniter.dm

@@ -12,8 +12,7 @@
 	sparks.attach(src)
 
 /obj/item/device/assembly/igniter/Destroy()
-	qdel(sparks)
-	sparks = null
+	QDEL_NULL(sparks)
 	return ..()
 
 

code/modules/assembly/infrared.dm

@@ -255,9 +255,7 @@
 /obj/effect/beam/i_beam/Destroy()
 	if(master.first == src)
 		master.first = null
-	if(next)
-		qdel(next)
-		next = null
+	QDEL_NULL(next)
 	if(previous)
 		previous.next = null
 		master.last = previous

code/modules/assembly/shock_kit.dm

@@ -10,10 +10,8 @@
 	flags = CONDUCT
 
 /obj/item/assembly/shock_kit/Destroy()
-	qdel(part1)
-	part1 = null
-	qdel(part2)
-	part2 = null
+	QDEL_NULL(part1)
+	QDEL_NULL(part2)
 	return ..()
 
 /obj/item/assembly/shock_kit/attackby(obj/item/weapon/W as obj, mob/user as mob, params)