Is saying "nothing" considered a lie when someone is asked about the cause of their worry or sadness, and they do not wish to disclose it?

A person's statement, "Nothing," to someone who asks, "What's wrong with you?" is permissible and is not considered a forbidden lie. This is because its meaning is: "Nothing worth mentioning," or "Nothing that concerns the questioner," or "Nothing that matters to them." This falls under the category of tawriyah (equivocation), where the listener understands the opposite of what the speaker intends, for "in ambiguous statements there is a way out of lying."