Merge pull request #10238 from Ghommie/Ghommie-cit478

Brings in some mapping code updates.

code/game/turfs/change_turf.dm

@@ -1,6 +1,7 @@
 // This is a list of turf types we dont want to assign to baseturfs unless through initialization or explicitly
 GLOBAL_LIST_INIT(blacklisted_automated_baseturfs, typecacheof(list(
 	/turf/open/space,
+	/turf/baseturf_bottom
 	)))
 
 /turf/proc/empty(turf_type=/turf/open/space, baseturf_type, list/ignore_typecache, flags)
@@ -56,12 +57,20 @@ GLOBAL_LIST_INIT(blacklisted_automated_baseturfs, typecacheof(list(
 // Creates a new turf
 // new_baseturfs can be either a single type or list of types, formated the same as baseturfs. see turf.dm
 /turf/proc/ChangeTurf(path, list/new_baseturfs, flags)
-	if(!path)
-		return
-	if(path == /turf/open/space/basic)
-		// basic doesn't initialize and this will cause issues
-		// no warning though because this can happen naturaly as a result of it being built on top of
-		path = /turf/open/space
+	switch(path)
+		if(null)
+			return
+		if(/turf/baseturf_bottom)
+			path = SSmapping.level_trait(z, ZTRAIT_BASETURF) || /turf/open/space
+			if (!ispath(path))
+				path = text2path(path)
+				if (!ispath(path))
+					warning("Z-level [z] has invalid baseturf '[SSmapping.level_trait(z, ZTRAIT_BASETURF)]'")
+					path = /turf/open/space
+		if(/turf/open/space/basic)
+			// basic doesn't initialize and this will cause issues
+			// no warning though because this can happen naturaly as a result of it being built on top of
+			path = /turf/open/space
 	if(!GLOB.use_preloader && path == type && !(flags & CHANGETURF_FORCEOP)) // Don't no-op if the map loader requires it to be reconstructed
 		return src
 	if(flags & CHANGETURF_SKIP)
@@ -214,7 +223,7 @@ GLOBAL_LIST_INIT(blacklisted_automated_baseturfs, typecacheof(list(
 			newT.assemble_baseturfs(initial(fake_turf_type.baseturfs)) // The baseturfs list is created like roundstart
 			if(!length(newT.baseturfs))
 				newT.baseturfs = list(baseturfs)
-			newT.baseturfs -= newT.baseturfs & GLOB.blacklisted_automated_baseturfs
+			newT.baseturfs -= GLOB.blacklisted_automated_baseturfs
 			newT.baseturfs.Insert(1, old_baseturfs) // The old baseturfs are put underneath
 			return newT
 		if(!length(baseturfs))