Null pointer dereference (game crash) when rendering custom block

The game performs a null pointer dereference when attempting to render the custom block not found.

I have attached the add-on that causes this crash along with a video to showcase it and the null pointer dereference error.

I have tracked this crash down to be in the BlockGraphics::getTextureCarriedVariations function.

Steps to reproduce:

1. Import and enable the pack in a world
2. Run /give @s custom:block

Observed result:
The crash happens the second the game renders a block.

Expected result:
The game does not crash.