According to ChainCatcher, mempool data shows that miners mined an empty block at Bitcoin height 857116 (i.e., the block only contains one transaction, the block reward Coinbase).
Miners pack empty blocks for economic reasons, and this is the wisest choice for miners. In order to make full use of this time for mining and avoid conflicts with transactions packed in the parent block, miners cannot fill transactions into the block, which means that miners can only try to mine empty blocks.