How to use NBT tags on items for storing entities

I am trying to make an item that collects an entity and lets them out on right click and to collect them with a right click

I am making this mod, SPM(Super Pets Mod) and in this mod, there is a super pig and I want to collect it using a super collector item and for it to change texture when holding an entity but it doesn't work at all.

This is my Super Collector Item

This is my global variable

This is my value provider

This is my capture procedure

This is my release procedure

Could someone fix these?