V2.7

I know that's probably not the best place to post it, but I cant find any better way to report an issue.
And the issue is this:
In [1]: from pymongo import MongoClient
In [2]: m = MongoClient()
In [3]: mypass = ''
In [4]: isinstance(mypass, basestring)
Out [4]: True
In [5]: m.admin.authenticate('myuser', mypass)
....
....
 File "/usr/local/lib/python2.7/dist-packages/pymongo/auth.py", line 215, in _authenticate_mongo_cr
    key = _auth_key(nonce, username, password)
  File "/usr/local/lib/python2.7/dist-packages/pymongo/auth.py", line 76, in _auth_key
    digest = _password_digest(username, password)
  File "/usr/local/lib/python2.7/dist-packages/pymongo/auth.py", line 60, in _password_digest
    "of %s" % (basestring.__name__,))
TypeError: password must be an instance of basestring

In pymongo/auth.py: 

def _password_digest(username, password):
    """Get a password digest to use for authentication.
    """
    if not isinstance(password, basestring):
        raise TypeError("password must be an instance "
                        "of %s" % (basestring.__name__,))
....
How is this possible?