'NoneType' object has no attribute error, when using Kivy Screens

[chelovek]

on_dropfile does not return anything so by default it returns None.

https://github.com/kivy/kivy/blob/master...ropfile.py

Thanks. One thing I'm confused about is, the functions seem to work in this code above, but when I modify things a bit (adding screens, but leaving the core drop functions intact) it stops working.