Remove customer tax id required for Poland

addons/pl/favat/bill.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cbc"
+	"github.com/invopop/gobl/l10n"
 	"github.com/invopop/gobl/org"
 	"github.com/invopop/gobl/rules"
 	"github.com/invopop/gobl/rules/is"
@@ -72,11 +73,11 @@ func billInvoiceRules() *rules.Set {
 		rules.When(is.Func("not simplified", invoiceNotSimplified),
 			rules.Field("customer",
 				rules.Assert("09", "customer is required", is.Present),
-				rules.Field("tax_id",
-					rules.Assert("10", "customer tax ID is required", is.Present),
-				),
 			),
 		),
+		rules.Assert("10", "customer Polish tax ID code is required",
+			is.Func("Polish customer tax ID code", invoiceCustomerPLTaxIDCodePresent),
+		),
 		// Customer JST identity check (invoice-level, needs both customer.ext and customer.identities)
 		rules.Assert("11",
 			fmt.Sprintf("customer requires identity with role '%s' and code for JST", cbc.Code("8")),
@@ -121,6 +122,19 @@ func invoiceNotSimplified(val any) bool {
 	return !inv.HasTags(tax.TagSimplified)
 }
 
+// invoiceCustomerPLTaxIDCodePresent returns false when the customer has a
+// Polish tax ID but no code — the NIP is mandatory for Polish entities.
+func invoiceCustomerPLTaxIDCodePresent(val any) bool {
+	inv, ok := val.(*bill.Invoice)
+	if !ok || inv == nil || inv.Customer == nil || inv.Customer.TaxID == nil {
+		return true
+	}
+	if inv.Customer.TaxID.Country == l10n.PL.Tax() {
+		return len(inv.Customer.TaxID.Code) > 0
+	}
+	return true
+}
+
 func invoiceCustomerJSTIdentityValid(val any) bool {
 	inv, ok := val.(*bill.Invoice)
 	if !ok || inv == nil || inv.Customer == nil {

addons/pl/favat/bill_test.go

@@ -587,12 +587,38 @@ func TestSimplifiedInvoiceCustomerValidation(t *testing.T) {
 }
 
 func TestCustomerTaxIDValidation(t *testing.T) {
-	t.Run("customer without tax ID", func(t *testing.T) {
+	t.Run("customer without tax ID is valid", func(t *testing.T) {
 		inv := standardInvoice()
 		inv.Customer.TaxID = nil
 		require.NoError(t, inv.Calculate())
 		err := rules.Validate(inv)
-		assert.ErrorContains(t, err, "customer tax ID is required")
+		assert.NoError(t, err)
+	})
+
+	t.Run("Polish customer with tax ID code is valid", func(t *testing.T) {
+		inv := standardInvoice()
+		require.NoError(t, inv.Calculate())
+		err := rules.Validate(inv)
+		assert.NoError(t, err)
+	})
+
+	t.Run("Polish customer with empty tax ID code is invalid", func(t *testing.T) {
+		inv := standardInvoice()
+		inv.Customer.TaxID.Code = ""
+		require.NoError(t, inv.Calculate())
+		err := rules.Validate(inv)
+		assert.ErrorContains(t, err, "customer Polish tax ID code is required")
+	})
+
+	t.Run("non-Polish customer with empty tax ID code is valid", func(t *testing.T) {
+		inv := standardInvoice()
+		inv.Customer.TaxID = &tax.Identity{
+			Country: "DE",
+			Code:    "",
+		}
+		require.NoError(t, inv.Calculate())
+		err := rules.Validate(inv)
+		assert.NoError(t, err)
 	})
 }