The bug
Summoning a stack of mobs with a mob on bottom, an item frame in the middle, and a mob on top - a bee for example - will crash the game when the item frame breaks.
How to reproduce
Use this command:
/summon wolf ~ ~ ~ {Passengers:[{id:"item_frame",Passengers:[{id:"bee"}]}]}
Wait for the item frame to break
→ ❌ Game crashes
Crash report
19w34a\: [^crash-2019-08-22_16.15.31-server.txt]
Description: Ticking entity
java.lang.IllegalStateException: Unable to get Y-rotated facing of down
at fb.e(SourceFile:178)
at ajx.B(SourceFile:1733)
at ajx.j(SourceFile:2421)
at ajo.aa(SourceFile:397)
at ajx.aa(SourceFile:291)
at ajy.aa(SourceFile:227)
at ajo.h(SourceFile:390)
at ajx.h(SourceFile:2057)
at ajy.h(SourceFile:294)
at ata.h(SourceFile:219)
at ajo.aN(SourceFile:1648)
at ajx.aN(SourceFile:2427)
at wj.a(SourceFile:613)
at wj.a(SourceFile:620)
at wj.a(SourceFile:591)
at wj$$Lambda$2703/1685559517.accept(Unknown Source)
at bit.a(SourceFile:675)
at wj.a(SourceFile:386)
at net.minecraft.server.MinecraftServer.b(SourceFile:836)
at net.minecraft.server.MinecraftServer.a(SourceFile:775)
at ebt.a(SourceFile:128)
at net.minecraft.server.MinecraftServer.run(SourceFile:643)
at java.lang.Thread.run(Thread.java:745)
this is such a ridiculously specific bug. how do people even find things like this?