---- Minecraft Crash Report ----
// There are four lights!

Time: 20/05/20 9:55 AM
Description: Exception in server tick loop

java.lang.IllegalArgumentException: value already present: chf@6204b89e
	at com.google.common.collect.HashBiMap.put(HashBiMap.java:287)
	at com.google.common.collect.HashBiMap.put(HashBiMap.java:262)
	at gg.a(SourceFile:51)
	at gg.a(SourceFile:62)
	at gl$a.a(SourceFile:28)
	at net.minecraft.server.MinecraftServer.a(SourceFile:407)
	at net.minecraft.server.MinecraftServer.i_(SourceFile:334)
	at enr.d(SourceFile:65)
	at net.minecraft.server.MinecraftServer.run(SourceFile:666)
	at java.lang.Thread.run(Thread.java:745)


A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
	Minecraft Version: 20w21a
	Minecraft Version ID: 20w21a
	Operating System: Windows 7 (amd64) version 6.1
	Java Version: 1.8.0_51, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 1528227904 bytes (1457 MB) / 1979711488 bytes (1888 MB) up to 2147483648 bytes (2048 MB)
	CPUs: 8
	JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
	Player Count: 0 / 8; []
	Data Packs: vanilla
	Type: Integrated Server (map_client.txt)
	Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.