[MC-227537] Crash: java.lang.NullPointerException: Cannot invoke "it.unimi.dsi.fastutil.objects.ObjectSet.remove(Object)" because "$$4" is null

The bug

I received the error java.lang.NullPointerException: Cannot invoke "it.unimi.dsi.fastutil.objects.ObjectSet.remove(Object)" because "$$4" is null in my game's log today. I am unsure of the cause of the issue, because I wasn't monitoring my game's log at the time.

As of 1.18 Pre-release 7, this causes a crash.

Exception in server tick loop
java.lang.NullPointerException: Cannot invoke "it.unimi.dsi.fastutil.objects.ObjectSet.remove(Object)" because "$$4" is null
	at adb.b(SourceFile:230)
	at acv.a(SourceFile:1044)
	at adg.a(SourceFile:457)
	at aea.a(SourceFile:927)
	at vp.a(SourceFile:114)
	at vp$a.a(SourceFile:42)
	at qt.a(SourceFile:21)
	at yx.run(SourceFile:18)
	at auh.c(SourceFile:151)
	at aul.c(SourceFile:23)
	at net.minecraft.server.MinecraftServer.b(SourceFile:780)
	at net.minecraft.server.MinecraftServer.c(SourceFile:162)
	at auh.y(SourceFile:125)
	at net.minecraft.server.MinecraftServer.bf(SourceFile:762)
	at net.minecraft.server.MinecraftServer.y(SourceFile:756)
	at auh.bp(SourceFile:110)
	at net.minecraft.server.MinecraftServer.x(SourceFile:740)
	at net.minecraft.server.MinecraftServer.w(SourceFile:688)
	at net.minecraft.server.MinecraftServer.a(SourceFile:270)
	at java.base/java.lang.Thread.run(Thread.java:833)