I am not the most experienced person here. I will offer my input anyways.
There are a few different reasons why your opponents would donk-lead into you on a monotone board.
1. They flopped a small flush, and they are trying to protect it.
2. They have something like TP, 2P, a set, and they don't want you to blow them off the hand.
3. They have a monster draw, like 1 of that suit, and they want to set their own price to draw and/or just make you fold.
4. Least likely of all scenarios, they are bluffing
and want to make you fold because the board is scary.
Now, if you flop nothing at all, no pair, no draw, etc, why would you ever just call? Even if villain has nothing, what will calling accomplish? I would just fold if I didn't connect with the board. Unless you have some really good read on villain, you can't continue. You have very little equity.
However, there might be a rare occurrence where you read villains soul or something and push him off the hand with a big bluff on the flop, or on a later street. But this is pretty risky. Just fold if you totally missed. Save yourself the money.
That is all.