Parse errors come with line number "None"

[rixx]

I've been trying to debug a faulty ics file, and vobject's parser was not helpful: All I ever got was ""In transformFromNative, unhandled exception on line None". If you search for "line None" in the issues here, you'll see more examples of people encountering this error.

It would be nice to see line numbers in error messages, but even just adjusting the error message would be helpful (because I thought the underlying cause might be a vobject bug due to the missing line number, so I spent a while stepping through vobject without need).