During the process of making a mod for Minecraft: Java Edition, I noticed a potential implementation error, while this currently doesn't effect gameplay it does affect mods and may affect gameplay further down the line.

Currently it is possible to input items, which return false for Item#canFitInsideContainerItems, into shulker boxes via hoppers.
This is not a problem when inserting items using the GUI since ShulkerBoxSlot correctly delegates to Item#canFitInsideContainerItems while ShulkerBoxBlockEntity#canPlaceItemThroughFace specifically checks if the items block representation is ShulkerBoxBlock.
The fix would probably just be making ShulkerBoxBlockEntity#canPlaceItemThroughFace delegate to Item#canFitInsideContainerItems as well.

All code mentions use official mappings for version 1.19