How to handle zero id values ?

[Dev_Guy]

I'm developing a library that is basically a wrapper for the different PS resources.

The thing is that looking at the values returned by some resources I have noticed that sometimes I receive a zero value as the identifier of a resource.

For example: If I call the addresses resource I receive a Json with the following form:

{
	"address": {
		"id": 2,
		"id_customer": "2",
		"id_manufacturer": "0",
		"id_supplier": "0",
		"id_warehouse": "0",
		"id_country": "8",
		"id_state": "0",
		"alias": "Mon adresse",
		"company": "My Company",
		"lastname": "DOE",
		"firstname": "John",
		"vat_number": "",
		"address1": "16, Main street",
		"address2": "2nd floor",
		"postcode": "75002",
		"city": "Paris ",
		"other": "",
		"phone": "0102030405",
		"phone_mobile": "",
		"dni": "",
		"deleted": "0",
		"date_add": "2021-09-03 20:40:16",
		"date_upd": "2021-09-03 20:40:16"
	}
}

As you can see in the example, the value of id_state is "0" but when I call the states resource with the value 0, it returns a 404 NOT FOUND code.

Reading the documentation, the value of id_state is isNullOrUnsignedId so I understand that if that resource does not exist it should return null instead of 0 right?

My question is, how should I interpret the value 0 in this context?

Additionally, it says that the value of id_state should be isNullOrUnsignedId but it actually returns a String with a numeric value. It's not a big problem but I don't understand why it's a String, in fact, the only really numeric value is the first one ("id"), the rest are Strings

I don't know if I'm doing something wrong or I'm misunderstanding something

Any clarification is welcome

Thank you very much and sorry for the inconvenience

Best Regards