[1.16.5] Container isn't holding my item

Heya,

I'm sure this is just a really silly error and I'm just missing it, but whenever I put my item in the desiccator container, it disappears if I exit the GUI for it.

I'm not quite sure what I'm doing wrong.  I followed a tutorial on it since I'm not yet well-versed in containers.

Here's the code for the container

  Here's the code for the screen

Here's the code for the tile entity

Any help or points in the right direction are much appreciated!