Created a world in 18w48a and now it will not reload, tried 2 times.

---- Minecraft Crash Report ----
// Don't be sad, have a hug! <3

Time: 11/29/18 6:45 PM
Description: Exception in server tick loop

java.util.concurrent.CompletionException: java.lang.AbstractMethodError: bxx$$Lambda$1068/1422562336.a(Lcom/mojang/datafixers/Dynamic;)Ljava/lang/Object;
at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:273)
at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:280)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1584)
at ui$$Lambda$2049/834403954.accept(Unknown Source)
at java.util.ArrayList.forEach(ArrayList.java:1249)
at ui.e(SourceFile:369)
at net.minecraft.server.MinecraftServer.q(SourceFile:641)
at net.minecraft.server.MinecraftServer.p(SourceFile:625)
at net.minecraft.server.MinecraftServer.a(SourceFile:422)
at dog.a(SourceFile:91)
at dog.d(SourceFile:107)
at net.minecraft.server.MinecraftServer.run(SourceFile:562)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.AbstractMethodError: bxx$$Lambda$1068/1422562336.a(Lcom/mojang/datafixers/Dynamic;)Ljava/lang/Object;
at yg.a(SourceFile:18)
at cat.<init>(SourceFile:44)
at bvl$a.<init>(SourceFile:29)
at bxc$$Lambda$1006/1600591903.load(Unknown Source)
at cax.a(SourceFile:86)
at bqu.a(SourceFile:614)
at bqu.a(SourceFile:229)
at ui.d(SourceFile:439)
at ui$$Lambda$2032/370628119.get(Unknown Source)
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1582)
... 10 more

A detailed walkthrough of the error, its code path and all known details is as follows:
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