This question already has an answer here:
If I start a node with a random network id and a custom data directory, I can create an account and start mining.
What I expected after starting the miner is that it won't be able to mine any blocks since there are no other nodes who are submitting transactions.
But, when I started the miner, it started to mine blocks continuously.
So, what does these blocks contain? How can a block be mined without any transactions?