Invalid function tags prevent world from loading

If a function tag is created that refers to a function that does not exist, the function will refuse to load. According to the logs, the game crashes, however the game just gets stuck on the "load world" screen and is uncloseable except from the task manager.

From the logfile:

00:46:00	launcher	Preparing to launch minecraft client for 17w49b
00:46:00	launcher	Checking installations.
00:46:00	launcher	Minecraft client 17w49b is ready to start.
00:46:00	launcher	Starting!
00:46:01	launcher	Using default game log configuration client-1.12.xml (outputs XML)
00:46:02	bmz	Setting user: PhilosophioStone
00:46:03	bnc	Skipping bad option: lastServer:
00:46:03	bmz	LWJGL Version: 3.1.2 build 29
00:46:04	sj	Reloading ResourceManager: Default
00:46:05	clr	Missing sound for event: minecraft:block.pumpkin.carve
00:46:05	clr	Starting up SoundSystem...
00:46:05	clr	Initializing No Sound
00:46:05	clr	(Silent Mode)
00:46:05	clr	OpenAL initialized.
00:46:06	clr	Sound engine started
00:46:08	ciq	Created: 1024x512 textures-atlas
00:46:10	com.mojang.text2speech.NarratorWindows	Narrator library for x64 successfully loaded
00:46:10	net.minecraft.realms.RealmsBridge	Realms module missing
00:46:54	aoq	Loaded 0 recipes
00:46:54	clh	Starting integrated minecraft server version 17w49b
00:46:54	clh	Generating keypair
00:46:54	sj	Reloading ResourceManager: Default, turing, turing_functions
00:46:55	aoq	Loaded 466 recipes
00:46:55	k	Loaded 509 advancements
00:46:56	nk	Loaded 14 custom command functions
00:46:56	net.minecraft.server.MinecraftServer	Encountered an unexpected exception
com.google.gson.JsonParseException: Unknown value 'tmf:'
	at ua$a.a(SourceFile:83)
	at ub.a(SourceFile:97)
	at nk.a(SourceFile:139)
	at sj.a(SourceFile:126)
	at nk.<init>(SourceFile:47)
	at qs.b(SourceFile:164)
	at clh.a(SourceFile:96)
	at clh.d(SourceFile:128)
	at net.minecraft.server.MinecraftServer.run(SourceFile:467)
	at java.lang.Thread.run(Thread.java:745)
00:46:56	net.minecraft.server.MinecraftServer	This crash report has been saved to: C:\Users\elyis\AppData\Roaming\.minecraft\profiles\experimental\crash-reports\crash-2017-12-08_00.46.56-server.txt
00:46:56	net.minecraft.server.MinecraftServer	Stopping server
00:46:56	net.minecraft.server.MinecraftServer	Saving players
00:46:56	net.minecraft.server.MinecraftServer	Saving worlds