[neilv]

Probably you want to avoid signing an agreement that could necessitate actively lying to someone else.

If already under such an agreement, find a way not to lie.

Being proactive can help. The first example that comes to mind was when a highly-placed colleague (who I trusted, and with whom I had a good rapport) asked me directly whether I knew whether of anyone in the department who was job-hunting. I didn't know of any, but I told them I generally couldn't answer that question, as a matter of policy. Because that's the kind of question for which we can anticipate a hard conflict someday, between betraying a trust, and lying to someone else. And that's an easy conflict to avoid.

"If I knew, I probably couldn't tell you." is a useful phrase.