When I tried to backup a 1.12.2 world or another pre release, the game crashes.

Here is the code line of the crash.

---- Minecraft Crash Report -------- Minecraft Crash Report ----// Don't be sad. I'll do better next time, I promise!
Time: 18-07-05 17:33Description: Exception in server tick loop
java.lang.NullPointerException: Exception in server tick loop at btd.<init>(SourceFile:13) at bte.b(SourceFile:328) at java.util.stream.ReferencePipeline$3$1.accept(Unknown Source) at java.util.stream.ReferencePipeline$3$1.accept(Unknown Source) at java.util.stream.ReferencePipeline$3$1.accept(Unknown Source) at java.util.Iterator.forEachRemaining(Unknown Source) at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Unknown Source) at java.util.stream.AbstractPipeline.copyInto(Unknown Source) at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source) at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(Unknown Source) at java.util.stream.AbstractPipeline.evaluate(Unknown Source) at java.util.stream.ReferencePipeline.collect(Unknown Source) at bte.a(SourceFile:329) at bng.n(SourceFile:81) at sz.q(SourceFile:594) at sz.<init>(SourceFile:126) at dfa.a(SourceFile:97) at dfa.d(SourceFile:132) at net.minecraft.server.MinecraftServer.run(SourceFile:507) at java.lang.Thread.run(Unknown Source)

A detailed walkthrough of the error, its code path and all known details is as follows:---------------------------------------------------------------------------------------
– System Details --Details: Minecraft Version: 1.13-pre6 Operating System: Windows 7 (amd64) version 6.1 Java Version: 1.8.0_171, Oracle Corporation Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation Memory: 208272568 bytes (198 MB) / 491859968 bytes (469 MB) up to 1038876672 bytes (990 MB) JVM Flags: 9 total; -XX:+UseConcMarkSweepGC -XX:-UseAdaptiveSizePolicy -XX:+CMSParallelRemarkEnabled -XX:+ParallelRefProcEnabled -XX:+CMSClassUnloadingEnabled -XX:+UseCMSInitiatingOccupancyOnly -Xmx1024M -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M Profiler Position: N/A (disabled) 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.#@Unable to render embedded object: File (@# Game crashed) not found. Crash report saved to: #@!@# C:\Users\Philippe\AppData\Roaming\.minecraft\crash-reports\crash-2018-07-05_17.33.18-server.txt[17:33:18] [Client Shutdown Thread/INFO]: Stopping server[17:33:18] [Client Shutdown Thread/INFO]: Saving players[17:33:18] [Client Shutdown Thread/INFO]: Saving worldsAL lib: (EE) alc_cleanup: 1 device not closed[L] Launcher stopped.[L] Minecraft closed with exit code: -1 (0xffffffff)