Add periodic cleaning of several player-containing lists to server tasks

code/controllers/subsystem/server_maint.dm

@@ -8,6 +8,7 @@ SUBSYSTEM_DEF(server_maint)
 	init_order = INIT_ORDER_SERVER_MAINT
 	runlevels = RUNLEVEL_LOBBY | RUNLEVELS_DEFAULT
 	var/list/currentrun
+	var/cleanup_ticker = 0
 
 /datum/controller/subsystem/server_maint/PreInit()
 	world.hub_password = "" //quickly! before the hubbies see us.
@@ -15,6 +16,8 @@ SUBSYSTEM_DEF(server_maint)
 /datum/controller/subsystem/server_maint/Initialize(timeofday)
 	if (CONFIG_GET(flag/hub))
 		world.update_hub_visibility(TRUE)
+	if(listclearnulls(GLOB.player_list)) // Do this here on the sly
+		log_world("Found a null in player_list!")
 	return ..()
 
 /datum/controller/subsystem/server_maint/fire(resumed = FALSE)
@@ -23,6 +26,32 @@ SUBSYSTEM_DEF(server_maint)
 			log_world("Found a null in clients list!")
 		src.currentrun = GLOB.clients.Copy()
 
+		switch (cleanup_ticker) // do only one of these per fire()
+			if (0)
+				if(listclearnulls(GLOB.player_list))
+					log_world("Found a null in player_list!")
+				cleanup_ticker++
+			if (5)
+				if(listclearnulls(GLOB.mob_list))
+					log_world("Found a null in mob_list!")
+				cleanup_ticker++
+			if (10)
+				if(listclearnulls(GLOB.alive_mob_list))
+					log_world("Found a null in alive_mob_list!")
+				cleanup_ticker++
+			if (15)
+				if(listclearnulls(GLOB.suicided_mob_list))
+					log_world("Found a null in suicided_mob_list!")
+				cleanup_ticker++
+			if (20)
+				if(listclearnulls(GLOB.dead_mob_list))
+					log_world("Found a null in dead_mob_list!")
+				cleanup_ticker++
+			if (25)
+				cleanup_ticker = 0
+			else
+				cleanup_ticker++
+
 	var/list/currentrun = src.currentrun
 	var/round_started = SSticker.HasRoundStarted()