@classmethod
def str_val(cls, val):
    """
        Format the value of a metric value to a string

        :param val: number to be formatted
        :return: a string with the formatted value
        """
    str_val = val
    if val is None:
        str_val = 'NA'
    elif type(val) == float:
        str_val = '%0.2f' % val
    else:
        str_val = str(val)
    return str_val
