[Roman_V_M]

This is just a guess, but most of the time I get this sort of error it is because one of my strings is None instead of a string. Try a "print repr(item)" at the end of your for loop and look for that in your log maybe.

Thanks for the hint. Indeed, the problem was in incomplete WIP code. As it turned out, Gotham allows to add ListItems without path property, while Frodo does not - it requires at least an empty string dummy. Adding paths solved the problem.