"Sweet Dreams" Advancement shows a checkered box instead of a bed

I expected to see a bed of some sort, but I found a checkered, bed-shaped box for the "Sweet Dreams" Advancement.

Steps to Recreate:
1. Unlock the Adventure advancement tree by killing a monster, trading with a villager, or sleeping in a bed.
2. Open the Adventure advancement tree.
3. Look at the "Sweet Dreams" bed advancement. It should be a checkered box because of the box.