public function setMasteryValue($masteryValue)
    {
        if (is_numeric($masteryValue) || (is_bool($masteryValue) && $masteryValue === false)) {
            $this->masteryValue = $masteryValue;
        } else {
            $msg = "MasteryValue must be a number or (boolean) false, '" . gettype($masteryValue) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }