Crash on viewing factuur without verantwoordelijke

[davidv1992]

Traceback (most recent call last):
File "main.py", line 31, in
mainloop(screenManager)
File "/home/david/madmin_cncz/madmin/factuurinfo/gui_lib/core.py", line 74, in mainloop
curses.wrapper(_mainloop)
File "/usr/lib/python2.7/curses/wrapper.py", line 43, in wrapper
return func(stdscr, _args, *_kwds)
File "/home/david/madmin_cncz/madmin/factuurinfo/gui_lib/core.py", line 63, in _mainloop
elif not _WindowWidget.keyEvent(key):
File "/home/david/madmin_cncz/madmin/factuurinfo/manager.py", line 9, in keyEvent
super(factuurManager,self).keyEvent(key)
File "/home/david/madmin_cncz/madmin/factuurinfo/gui_lib/displaystack.py", line 46, in keyEvent
self.pages[-1].keyEvent(key)
File "/home/david/madmin_cncz/madmin/factuurinfo/factuurList.py", line 47, in keyEvent
super(factuurList,self).keyEvent(key)
File "/home/david/madmin_cncz/madmin/factuurinfo/gui_lib/container.py", line 63, in keyEvent
return self.children[self.curFocus][2].keyEvent(key)
File "/home/david/madmin_cncz/madmin/factuurinfo/gui_lib/listbox.py", line 78, in keyEvent
return self.items[self.curFocus].keyEvent(key)
File "/home/david/madmin_cncz/madmin/factuurinfo/factuurList.py", line 24, in keyEvent
self.manager.push(factuurDetail(1,1,self.factuur, self.manager))
File "/home/david/madmin_cncz/madmin/factuurinfo/factuurDetail.py", line 96, in init
self.infobox = factuurInfobox(width,0,factuur)
File "/home/david/madmin_cncz/madmin/factuurinfo/factuurDetail.py", line 160, in init
self.verantwoordelijkeValue = Label(0,1,factuur['verantwoordelijke'].encode('utf-8'))
AttributeError: 'NoneType' object has no attribute 'encode'

[davidv1992]

Bug is in server, factuur/vereniging returns facturen with none value for verantwoordelijke