[MC-215215] Game crashes when loading a world with 21w05b default worldgen datapack

I have archived slicedlime's default world generation datapack of 21w05b and I tried to use it in 21w06a, to see if it would bring back the old world. But then the game crashed.

I have attached the crash report and the datapack I used for the world.

21w06a: crash-2021-02-12_15.35.03-server.txt

Description: Exception generating new chunk

java.lang.ArrayIndexOutOfBoundsException: -1
	at cjm.b(SourceFile:62)
	at cmq.a(SourceFile:363)
	at cjq.d(SourceFile:74)
	at cjq$$Lambda$1938/2128263493.doWork(Unknown Source)
	at cjq.a(SourceFile:231)
	at aai.a(SourceFile:563)
	at aai$$Lambda$4699/1909105080.apply(Unknown Source)
	at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
	at aai.a(SourceFile:557)
	at aai$$Lambda$4685/1447867729.apply(Unknown Source)
	at java.util.concurrent.CompletableFuture.uniCompose(CompletableFuture.java:952)
	at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:926)
	at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:442)
	at aak.b(SourceFile:58)
	at aak$$Lambda$4697/882589677.run(Unknown Source)
	at apb.e(SourceFile:84)
	at apb.a(SourceFile:124)
	at apb.run(SourceFile:92)
	at java.util.concurrent.ForkJoinTask$RunnableExecuteAction.exec(ForkJoinTask.java:1402)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1056)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1689)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)