validate tax exempt

message.xml

@@ -21,5 +21,8 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.message" id="msg_party_without_account_receivable">
             <field name="text">Party "%(s)s" has no any account receivable defined. Please, assign one. </field>
         </record>
+        <record model="ir.message" id="msg_dont_account_other_income">
+            <field name="text">Product "%(product)s" has no account other income defined in account category. Please, assign one. </field>
+        </record>
     </data>
 </tryton>

sale.py

@@ -263,13 +263,16 @@ class Sale(metaclass=PoolMeta):
                         sale=sale.rec_name))
         super(Sale, cls).delete(sales)
 
-    def _get_invoice_sale(self):
-        invoice = super(Sale, self)._get_invoice_sale()
-        invoice.reference = self.reference
-        invoice.description = self.description
-        invoice.comment = self.comment
-        invoice.shop = self.shop.id
-        invoice.invoice_type = self.invoice_type
+    def create_invoice(self):
+        invoice = super(Sale, self).create_invoice()
+        print('ingresa por este valor')
+        if invoice.shop and invoice.shop.tax_exempt:
+            for line in invoice.lines:
+                if not line.product.account_category.account_other_income:
+                    raise AccessError(
+                    gettext('sale_shop.msg_dont_account_other_income',
+                        product=line.product.rec_name))
+                line.account = line.product.account_category.account_other_income
         return invoice