Minor refactor of how gas IDs are handled

code/game/objects/effects/effect_system/effects_foam.dm

@@ -279,8 +279,9 @@
 				qdel(H)
 			var/list/G_gases = G.gases
 			for(var/I in G_gases)
-				if(I != "o2" && I != "n2")
-					G.gases[I][MOLES] = 0
+				if(I == /datum/gas/oxygen || I == /datum/gas/nitrogen)
+					continue
+				G_gases[I][MOLES] = 0
 			G.garbage_collect()
 			O.air_update_turf()
 		for(var/obj/machinery/atmospherics/components/unary/U in O)