diff --git a/account_payment_order/models/account_move_line.py b/account_payment_order/models/account_move_line.py
index 9e79d5e29..6824a9076 100644
--- a/account_payment_order/models/account_move_line.py
+++ b/account_payment_order/models/account_move_line.py
@@ -54,7 +54,7 @@ class AccountMoveLine(models.Model):
         communication = self.ref or self.name
         # change these default values if move line is linked to an invoice
         if self.move_id.is_invoice():
-            if self.move_id.reference_type != "none":
+            if (self.move_id.reference_type or "none") != "none":
                 communication = self.move_id.ref
                 ref2comm_type = aplo.invoice_reference_type2communication_type()
                 communication_type = ref2comm_type[self.move_id.reference_type]
diff --git a/account_payment_order/views/account_invoice_view.xml b/account_payment_order/views/account_invoice_view.xml
index 5b162ebb9..f705b70e2 100644
--- a/account_payment_order/views/account_invoice_view.xml
+++ b/account_payment_order/views/account_invoice_view.xml
@@ -45,10 +45,10 @@
             <field name="ref" position="before">
                 <field
                     name="reference_type"
-                    required="1"
                     nolabel="1"
                     attrs="{'readonly':[('state','!=','draft')],
-                               'invisible': [('type', 'not in', ('out_invoice', 'out_refund'))]}"
+                            'invisible': [('type', 'not in', ('out_invoice', 'out_refund'))],
+                            'required': [('type', 'in', ('out_invoice', 'out_refund'))]}"
                 />
             </field>
         </field>