Boolean for if mob is sleeping

There should be an NBT boolean for if a mob is sleeping. This would assist in sorting mobs that are sleeping or not, such as Villagers.

Currently in the game, you can discern the exact position of a mob's bed, but for the purposes of simply determining whether or not a mob is sleeping, the position is unnecessary. 

Practically speaking, in @e target selection, you can sort specifically by NBT tags, but not necessarily the lack thereof for integers. You can use ! to check if an integer NBT is not a specific value, but it'll still pass any other value.

/effect give @e[type=minecraft:villager,nbt={SleepingY:64}] minecraft:glowing 10 

This would give every villager sleeping at Y 64 the glowing effect, but there's no easy way to sort by villagers that are sleeping, regardless of their Y level. My proposition would be something along the lines of a boolean named "IsSleeping" so that you can easily check between if they're sleeping, 1, or if they aren't, 0.

For example, to sort for villagers that aren't sleeping:

/effect give @e[type=minecraft:villager,nbt={IsSleeping:0b}] minecraft:glowing 10

This would give every non-sleeping villager the glowing effect, and with this boolean, you'd be able to target select any villager depending on their sleeping status, not their exact sleeping position.