18w06a crash: Exception generating new chunk: java.util.concurrent.ExecutionException: java.lang.ClassCastException: axc cannot be cast to azb

The bug

The game can crash with the attached crash report when for example creating a superflat world with the preset below:

minecraft:stone,minecraft:sand,2*minecraft:air,minecraft:stone;2;biome_1,decoration

Crash report

18w06a\: [^crash-2018-02-11_11.31.54-server.txt]

Description: Exception generating new chunk

java.util.concurrent.ExecutionException: java.lang.ClassCastException: axc cannot be cast to azb
	at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2237)
	at rz.c(SourceFile:130)
	at atm.c(SourceFile:311)
	at atm.p(SourceFile:307)
	at atm.b(SourceFile:718)
	at atm.c(SourceFile:247)
	at atm.l(SourceFile:231)
	at bho.b(SourceFile:61)
	at sa.b(SourceFile:824)
	at sa.a(SourceFile:760)
	at cvl.a(SourceFile:98)
	at cvl.d(SourceFile:131)
	at net.minecraft.server.MinecraftServer.run(SourceFile:503)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassCastException: axc cannot be cast to azb
	at sf.f(SourceFile:169)
	at bpl.a(SourceFile:221)
	at bpl.b(SourceFile:175)
	at bpl.a(SourceFile:171)
	at boo.a(SourceFile:63)
	at bpa.a(SourceFile:57)
	at bly.a(SourceFile:92)
	at bny.a(SourceFile:16)
	at bny.a(SourceFile:13)
	at bit.a(SourceFile:27)
	at aud.a(SourceFile:416)
	at bhz.b(SourceFile:142)
	at sn.a(SourceFile:13)
	at sm.a(SourceFile:34)
	at bgq.a(SourceFile:89)
	at sr.a(SourceFile:54)
	at sr.a(SourceFile:23)
	at zo$a.a(SourceFile:143)
	at zo$a$$Lambda$875/621712682.apply(Unknown Source)
	at java.util.concurrent.CompletableFuture$AsyncApply.exec(CompletableFuture.java:501)
	at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
	at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:902)
	at java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1689)
	at java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1644)
	at java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:157)