Summoning falling_block entities with BlockState NBT set to any air block (air, cave_air, void_air) default to sand

Steps to Reproduce:
1. Type this command into a command block or the chat:
/summon falling_block ~ ~2 ~ {Time:1,BlockState:{Name:"minecraft:air"}}

The summoned entity will default to sand instead of air.

Likely related to MC-124728