One of my players reported that when she "right clicked without shift on a llama it crashed." She was playing on our SMP server and was disconnected, but the server was unaffected. I have been able to replicate this in singleplayer. She reports she was holding an enchanted diamond sword, and I used an empty hand. I was using an un-tamed llama, if that matters.

Here is her crash:
crash-2019-07-04_20.53.33-client.txt

And here is mine: https://paste.dimdev.org/okeqacezim.mccrash
My latest.log was too long to pastebin, so here's an excerpt: https://pastebin.com/qJB7cWrT

My versions are:
Quark: Quark-r1.5-166
AutoRegLib: AutoRegLib-1.3-31
Forge: forge-1.12.2-14.23.5.2838-universal
Full Modlist: http://enthusiasticraft.cf/modpack-update-1-5-4-hotfix/#modlist

I just checked and realized I'm technically one version outdated on Quark, which means that I'm violating the rule of not using the most recent version. However, I checked the changelog and didn't see anything that seemed to apply to this issue, so I hope you will accept my report.

I actually fixed this, but it's a fair report.