[MC-175988] Dying without a valid spawnpoint causes a softlock

Workaround

Run /spawnpoint, and then close and reopen the world.

The bug

After dying and respawning in 20w13a without a valid spawn point, the game is in a softlocked state. The player will have a duplicated version of themselves standing at the same location, and they won't be able to move or interact with the world in any other way. This even persists after closing and reopening the world. This affects all game modes.

When this happens, the following will be printed into the game console:

Error executing task on Server
java.lang.NullPointerException
	at bns.l(SourceFile:173)
	at bns.d_(SourceFile:421)
	at aav.a(SourceFile:495)
	at zc.a(SourceFile:1216)
	at qv.a(SourceFile:30)
	at qv.a(SourceFile:8)
	at na.a(SourceFile:21)
	at ug.run(SourceFile:18)
	at akx.c(SourceFile:144)
	at alb.c(SourceFile:23)
	at net.minecraft.server.MinecraftServer.b(SourceFile:749)
	at net.minecraft.server.MinecraftServer.c(SourceFile:142)
	at akx.w(SourceFile:118)
	at net.minecraft.server.MinecraftServer.bc(SourceFile:731)
	at net.minecraft.server.MinecraftServer.w(SourceFile:725)
	at akx.c(SourceFile:127)
	at net.minecraft.server.MinecraftServer.v(SourceFile:710)
	at net.minecraft.server.MinecraftServer.run(SourceFile:662)
	at java.base/java.lang.Thread.run(Thread.java:835)

Error executing task on Server
java.lang.NullPointerException
	at yd.b(SourceFile:201)
	at xw.a(SourceFile:904)
	at yi.a(SourceFile:478)
	at zc.a(SourceFile:845)
	at ri.a(SourceFile:122)
	at ri$b.a(SourceFile:18)
	at na.a(SourceFile:21)
	at ug.run(SourceFile:18)
	at akx.c(SourceFile:144)
	at alb.c(SourceFile:23)
	at net.minecraft.server.MinecraftServer.b(SourceFile:749)
	at net.minecraft.server.MinecraftServer.c(SourceFile:142)
	at akx.w(SourceFile:118)
	at net.minecraft.server.MinecraftServer.bc(SourceFile:731)
	at net.minecraft.server.MinecraftServer.w(SourceFile:725)
	at akx.bm(SourceFile:103)
	at net.minecraft.server.MinecraftServer.v(SourceFile:709)
	at net.minecraft.server.MinecraftServer.run(SourceFile:662)
	at java.base/java.lang.Thread.run(Thread.java:835)

To reproduce

Run /spawnpoint @s ~ ~ ~ while in spectator mode somewhere underground (so that the spawnpoint would be blocked
Switch into Creative, Survival, or Adventure mode
Die
Respawn
→ Your game is in a softlocked state