diff --git a/modules/edocument_ubl/edocument.py b/modules/edocument_ubl/edocument.py
index 7e4b1b808b..ad15dc0f94 100644
--- a/modules/edocument_ubl/edocument.py
+++ b/modules/edocument_ubl/edocument.py
@@ -180,12 +180,14 @@ class Invoice(Model):
     @cached_property
     def sale_reference(self):
         if hasattr(self.invoice, 'sales'):
-            return ','.join(s.reference for s in self.invoice.sales)
+            return ','.join(
+                filter(None, (s.reference for s in self.invoice.sales)))
 
     @cached_property
     def sale_number(self):
         if hasattr(self.invoice, 'sales'):
-            return ','.join(s.number for s in self.invoice.sales)
+            return ','.join(
+                filter(None, (s.number for s in self.invoice.sales)))
 
     @property
     def taxes(self):