Python error in find_head_package on run_script of unittest/__init__.py

This is probably not something one would normally do but when done, it causes a problem:

Mac OS 10.6 (snow leopard)
Python 2.7 (apple default)

mg = ModuleGraph()
mg.run_script('/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/unittest/init.py'

produces AttributeError: 'NoneType' object has no attribute 'identifier'

Call stack is
run_script
scan_code
_safe_import_hook
import_hook
find_head_package