@classmethod
def rc_notfound(cls, interface_type, resource_name=None):
    """Exception used when no resource class is provided and no default is found.
        """
    msg = ('Resource class for %s not provided and default not found.' %
        interface_type)
    if resource_name:
        msg = "Could not parse '%s'. %s" % (resource_name, msg)
    return cls(msg)
