'Return a string in key=value&key=value form
Values of None are not included in the output string.
Args:
parameters:
A dict of (key, value) tuples, where value is encoded as
specified by self._encoding
Returns:
A URL-encoded string in "key=value&key=value" form'

def _EncodeParameters(self, parameters):

    if (parameters is None):
        return None
    else:
        return urllib.urlencode(dict([(k, self._Encode(v)) for (k, v) in parameters.items() if (v is not None)]))
