def _process_resources(resources):
    """ Return an argument to suppress normal Bokeh server resources, if requested.

    Args:
        resources ("default" or None) :
            If None, return an HTML argument to suppress default resources.

    Returns:
        str

    """
    if resources not in ("default", None):
        raise ValueError("`resources` must be either 'default' or None.")
    if resources is None:
        return "&resources=none"
    return ""