iOS8 - constraints ambiguously suggest a height of zero

Question

Has anyone got any idea how to debug this?

Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview c

Answer 1

In my case, it is because I'm designing the cell with xib, and I forget to add that xib file to the target.

After I add that xib file to the target, the problem is gone