Minecraft Version: 1.12.2

GrimPack Version: 6.0.0.1

Forge Version: 14.23.5.2768

I captured a treasure mob using an Ender IO soul vile and put it in a powered spawner. When the powered spawner tries to spawn the mob it gets a null pointer exception and crashes the client. here is the crash report. https://pastebin.com/ihGt27Qb

Closing as GrimPack is no longer maintained.

Sorry it took me a while to reply.
I did not use creative for anything. I was able to reproduce it in a single player world.
The mods I had in the pack I reproduced it in where
Biomes O' Plenty: 7.0.1.2399
Ender IO: 5.0.37
EnderCore: 0.5.43
Grim Pack: 6.0.0.6
Just Enough Items: 4.13.1.22
Mekanism: 9.4.13.349

Steps,
I created a new world using the Biomes O' Plenty world gen (though I don't think that matters)
I used a spawn egg to spawn a Treasure Mob.
I gave myself an empty soul vile from Ender IO
I changed out of creative into survival
I used the soul vile to capture the treasure mob.
I changed back into survival.
I gave myself a broken spawner from Ender IO, a Soul Binder from Ender IO, a capacitor from Ender IO, and a fully charged energy cube from mechanism
I placed the energy cube and the soul binder next to each other (to power the soul binder)
I put the treasure mob soul vile and broken spawner in the soul binder and click the enchantment bottle button to start it.
Once it finished I took the broken spawner out of the soul binder.
I gave myself a vanilla anvil and a non creative Ender IO powered spawner, and another capacitor from Ender IO.
I combined the powered spawner and the broken spawner in the vanilla anvil.
I then placed the powered spawner next to the mechanism energy cube and then put the capacitor in it. A second or two after doing so my game crashed with that error.

Let me know if you still need more details.

Just tested it and wasn't able to reproduce.

Was this in Singleplayer of Multiplayer?
Were you doing anything special?
Does this happen every time?

When I tested I was using the creative spawner is this different to the one you were using besides the creative aspect?

I am not that familiar with Ender IO so any other information helps.