public function applyDiscountForPricePerUnitOfMeasure(?Discount $discount = null): ?string 	{ 		if (!$discount || !$this->price_per_unit_of_measure) { 			return null; 		}  		return $discount->is_percentage ? MathMoneyOperations::calculate($this->price_per_unit_of_measure, MathMoneyOperations::calculate($this->price_per_unit_of_measure, MathMoneyOperations::calculate((string) $discount->amount, '100', '/'), '*'), '-') : MathMoneyOperations::calculate($this->price_per_unit_of_measure, (string) $discount->amount, '-'); 	}