Posestand throws Exception when /lockstand with book
How to reproduce:
1. Place armorstand
2. add arms with /posestand givearms
3. remove base with /posestand togglebase
4. add items to posestand
5. swap hands with /posestand swaphands
6. add book to main hand
7. lock posestand with /lockstand
Error is thrown:
{width="900" height="209"}