Attempt to import an optional dependency.

    Silently returns None if the requested module is not available.

    Args:
        mod_name (str) : name of the optional module to try to import

    Returns:
        imported module or None, if import fails

def import_optional(mod_name):
    ''' Attempt to import an optional dependency.

    Silently returns None if the requested module is not available.

    Args:
        mod_name (str) : name of the optional module to try to import

    Returns:
        imported module or None, if import fails

    '''
    try:
        return import_module(mod_name)
    except ImportError:
        pass
    except Exception:
        msg = "Failed to import optional module `{}`".format(mod_name)
        log.exception(msg)