[MC-132248] Server crash on launch using Java 9 or newer

The bug

Server does not launch using Java 10. It was working fine before 1.13-pre5 (1.13-pre4 included). I included the log of the crash. Both OpenJDK and Oracle's JRE are affected. This issue does not seem to occur when using Java 8.

[16:53:37] [Bootstrap 0/ERROR]: Unable to build datafixers
java.util.ConcurrentModificationException: null
	at java.util.HashMap.computeIfAbsent(HashMap.java:1139) ~[?:?]
	at com.mojang.datafixers.DSL.taggedChoiceType(DSL.java:251) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.TaggedChoice.lambda$null$1(TaggedChoice.java:72) ~[server.jar:?]
	at java.util.HashMap.computeIfAbsent(HashMap.java:1138) ~[?:?]
	at com.mojang.datafixers.types.templates.TaggedChoice.lambda$apply$2(TaggedChoice.java:71) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Named.lambda$apply$0(Named.java:43) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Check$1.apply(Check.java:45) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Sum$1.apply(Sum.java:50) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Sum$1.apply(Sum.java:50) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Sum$1.apply(Sum.java:50) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.Sum$1.apply(Sum.java:50) ~[server.jar:?]
	at com.mojang.datafixers.types.families.RecursiveTypeFamily.lambda$null$1(RecursiveTypeFamily.java:107) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.RecursivePoint$RecursivePointType.unfold(RecursivePoint.java:132) ~[server.jar:?]
	at com.mojang.datafixers.types.templates.RecursivePoint$RecursivePointType.findCheckedType(RecursivePoint.java:183) ~[server.jar:?]
	at com.mojang.datafixers.schemas.Schema.getType(Schema.java:80) ~[server.jar:?]
	at com.mojang.datafixers.DataFixerBuilder.lambda$build$1(DataFixerBuilder.java:68) ~[server.jar:?]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1135) ~[?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) ~[?:?]
	at java.lang.Thread.run(Thread.java:844) [?:?]

Code analysis

Code analysis by [Mod] Pokechu22 in this comment.