Fixes a runtime when creating a new disposal after roundstart

code/modules/recycling/disposal.dm

@@ -27,12 +27,10 @@
 	idle_power_usage = 100
 
 // create a new disposal
-// find the attached trunk (if present) and init gas resvr.
+// find the attached trunk (if present)
 /obj/machinery/disposal/New()
 	..()
 	trunk_check()
-
-	air_contents = new/datum/gas_mixture()
 	//gas.volume = 1.05 * CELLSTANDARD
 	update()
 
@@ -59,6 +57,7 @@
 	var/datum/gas_mixture/env = new
 	env.copy_from(L.return_air())
 	var/datum/gas_mixture/removed = env.remove(SEND_PRESSURE + 1)
+	air_contents = new
 	air_contents.merge(removed)
 	trunk_check()