TypeError: 'NoneType' object is not iterable

C:UsersJinxDesktopUTRLabos1>sim.py < test.txt
['stanje1']
['st6']
Traceback (most recent call last):
File "C:UsersJinxDesktopUTRLabos1sim.py", line 50, in <module>
    print(automaton(['stanje1'], inputArrays[0], transitionFunction))
File "C:UsersJinxDesktopUTRLabos1sim.py", line 45, in automaton
    if estates : other = automaton(estates, ir[1:], fn)
File "C:UsersJinxDesktopUTRLabos1sim.py", line 37, in automaton
    states += eNKA(s, ir[0], fn)
TypeError: 'NoneType' object is not iterable

states += eNKA(s, ir[0], fn)