Miners don't broadcast blocks (even empty blocks) unless they are mined (hashed with the current difficulty). Even though the block is "empty", there's still the coinbase transaction (the transaction that pays the block reward to the miner) and other information in the block header like the hash of the previous block and the nonce.

So, an empty block on the blockchain is still mined, and isn't really "empty" at all. It's void of transactions other than the coinbase transaction.