SetAvatar.
        [Preview API]
        :param :class:`<Avatar> <azure.devops.v5_1.graph.models.Avatar>` avatar:
        :param str subject_descriptor:

def set_avatar(self, avatar, subject_descriptor):
        """SetAvatar.
        [Preview API]
        :param :class:`<Avatar> <azure.devops.v5_1.graph.models.Avatar>` avatar:
        :param str subject_descriptor:
        """
        route_values = {}
        if subject_descriptor is not None:
            route_values['subjectDescriptor'] = self._serialize.url('subject_descriptor', subject_descriptor, 'str')
        content = self._serialize.body(avatar, 'Avatar')
        self._send(http_method='PUT',
                   location_id='801eaf9c-0585-4be8-9cdb-b0efa074de91',
                   version='5.1-preview.1',
                   route_values=route_values,
                   content=content)