This is common practice, but it’s playing into a bad power dynamic where the employer is trying to anchor the negotiation to a number. It’s a predatory question, and giving a bullshit answer to a bullshit question is a reasonable response.

As I mentioned in another comment, I personally prefer just setting a salary range I’d be willing to accept. I walk away if given an offer below that range. It gives me the initiative of anchoring the negotiation to a number I want.

It also saves me a lot of time by screening out companies that aren’t willing to actually negotiate.