public static function fullJoinWithout(TimeSlot $a, TimeSlot $b) {

        // Initialize the time slots.
        $leftJoins  = static::leftJoinWithout($a, $b);
        $rightJoins = static::rightJoinWithout($a, $b);

        // Check the time slots.
        if (null === $leftJoins && null === $rightJoins) {
            return null;
        }
        if (null === $leftJoins) {
            return $rightJoins;
        }
        if (null === $rightJoins) {
            return $leftJoins;
        }

        // Return the time slots.
        return static::sort(array_merge($leftJoins, $rightJoins));
    }