[Investigating] Server crash and player lockout when dispelling spell

[karcsesz]

Hello there ^c^

@ryze312 recently ran into a pretty severe issue when trying to dispel a spell she cast as a unicorn on a server I've set up.

The entire server crashed with the following error log, and after it recovered, she could not rejoin due to invalid player data.

minecraft-1  | [21:20:28] [Server thread/ERROR]: Couldn't place player in world
minecraft-1  | net.minecraft.class_148: Loading entity NBT
[snip]
minecraft-1  | Caused by: java.lang.NullPointerException
minecraft-1  | at java.util.Objects.requireNonNull(Objects.java:208) ~[?:?]
minecraft-1  | at java.util.ImmutableCollections$List12.<init>(ImmutableCollections.java:556) ~[?:?]
minecraft-1  | at java.util.List.of(List.java:812) ~[?:?]
minecraft-1  | at com.minelittlepony.unicopia.ability.magic.spell.PlaceableSpell.getDelegates(PlaceableSpell.java:106) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.ability.magic.spell.AbstractDelegatingSpell.isDirty(AbstractDelegatingSpell.java:88) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.ability.magic.spell.SpellReference.hasDirtySpell(SpellReference.java:26) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.network.datasync.SpellNetworkedReference.isDirty(SpellNetworkedReference.java:46) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.network.datasync.SpellNetworkedReference.fromNbt(SpellNetworkedReference.java:35) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.network.datasync.NetworkedReferenceSet.lambda$fromNbt$5(NetworkedReferenceSet.java:122) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at java.util.ArrayList.forEach(ArrayList.java:1511) ~[?:?]
minecraft-1  | at com.minelittlepony.unicopia.network.datasync.NetworkedReferenceSet.fromNbt(NetworkedReferenceSet.java:120) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.network.datasync.EffectSync.fromNBT(EffectSync.java:191) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at com.minelittlepony.unicopia.entity.Living.fromNBT(Living.java:595) ~[Unicopia-1.3.0+1.20.2.jar:?]
minecraft-1  | at net.minecraft.class_1309.handler$bam001$unicopia$onReadCustomDataFromTag(class_1309.java:9358) ~[server-intermediary.jar:?]
[snip]

I've looked inside her player.dat and it seems like her character ended up with a spell under ./unicopia_caster/spells that has an empty spell collection.

Deleting that spell using NBTExplorer let her join, but casting it once again crashed the server and caused the same error when rejoining.

[ryze312]

Looks like the crash only occurs when trying to dispel scorching from the graph view., the one that opens up when pressing V key by default. Dispelling by holding V works as expected.

[Sollace]

I'm already aware of this issue. It's been fixed in development and will be part of the 1.3.1 update once I can get to fixing a couple other bugs. ^-^