raise KeyError in python

While running a python script (not mine), I get this error

  File "/home/mahmood/parboil/driver/process.py", line 74, in makefile    for makeargs in os.environ['MAKE_ARGS'].split(" "):  File "/usr/lib/python2.7/UserDict.py", line 40, in __getitem__    raise KeyError(key)
KeyError: 'MAKE_ARGS'

I don't understand what is the problem exactly? Is MAKE_ARGS something unknown for 2.7? This file is called from upper level files and I am trying to understand it for further debugging. Any idea?