gistfile1.txt

$ VIRTUALENV_VERSION=16.2.0 virtualenv .
Traceback (most recent call last):
  File "/usr/bin/virtualenv", line 11, in <module>
    sys.exit(main())
  File "/usr/lib/python2.7/site-packages/virtualenv.py", line 704, in main
    options, args = parser.parse_args()
  File "/usr/lib/python2.7/optparse.py", line 1384, in parse_args
    values = self.get_default_values()
  File "/usr/lib/python2.7/site-packages/virtualenv.py", line 579, in get_default_values
    return optparse.Values(defaults)
  File "/usr/lib/python2.7/optparse.py", line 841, in __init__
    setattr(self, attr, val)
TypeError: attribute name must be string, not 'NoneType'