fixed the complex typing.List[str] problem in imr.py fixes #129

[Eshan-Jogwar]

the imr.py at the place of error expected a Leaf class which has a value of type string. The fix uses unicode() function on the Node class to generate a string from all the Leaf classes which are part of the Node instance there to generate the string required at the place.

as i could figure out the function unicode() joins the value from all the Leaf Nodes part of the Node instance.

the code is handled as a run time exception by try and except in imr.py line 52.

fixes #129