Cullface on the tops and bottoms of glass panes causes crashing.

The bug

When adding cullface to the tops of bottoms of glass panes, the game crashes. It is yet to be discovered if this affects any other blocks.

How to reproduce

1. Create a resourcepack that tries to add cullface to the tops or bottoms of glass panes

2. Open the game

3. Place a glass pane, and then the game crashes.

Crash report

17w47a\: [^crash-2017-11-23_15.17.05-client.txt]

Description: Tesselating block model

java.lang.IllegalArgumentException: Cannot get property null as it does not exist in bal{block=minecraft:glass_pane, properties=[east, north, south, west]}
	at bal$a.c(SourceFile:174)
	at auw.c(SourceFile:65)
	at bal$a.c(SourceFile:380)
	at bzz.c(SourceFile:94)
	at bzz.a(SourceFile:44)
	at bzx.a(SourceFile:62)
	at ccb.b(SourceFile:180)
	at cbx.a(SourceFile:100)
	at cbw.b(SourceFile:140)
	at bzj.a(SourceFile:925)
	at bzc.b(SourceFile:1158)
	at bzc.a(SourceFile:1093)
	at bzc.a(SourceFile:951)
	at bmg.b(SourceFile:810)
	at bmg.a(SourceFile:369)
	at net.minecraft.client.main.Main.main(SourceFile:134)