Item validation fails if unitPrice is 0

[mpesari]

The OpenAPI specification states for item.unitPrice:

    Item:
      type: object
      required:
        - unitPrice
        - units
        - vatPercentage
        - productCode
      properties:
        unitPrice:
          type: integer
          format: int64
          example: 1590
          minimum: 0
          maximum: 99999999
          description: Unit price of an item in currency minor unit, eg. EUR cents. VAT should be included in amount unless `usePricesWithoutVat` is set to true.

The API accepts items with unitPrice = 0, but Paytrail\SDK\Model\Item validation fails:

paytrail-php-sdk/src/Model/Item.php

Lines 379 to 381 in c1df05e

	if (empty($props['unitPrice'])) {
	throw new ValidationException('Item unitPrice is empty');
	}

This was changed in SDK version 2.5.1 (#74)

Which behaviour is correct, SDK or API?

[VuorelaJ-P]

API is correct, validation should be done against only null value. Will fix. For refunds, amount should be positive not zero, since zero amount refund is not refund at all.