diff --git a/product/ERP5Type/Core/AcquiredProperty.py b/product/ERP5Type/Core/AcquiredProperty.py
index 4946e8966dba64d0f8900667b60f55afb6730f66..2be9e67f5429f5962e77f045e5b240751f3c17d9 100644
--- a/product/ERP5Type/Core/AcquiredProperty.py
+++ b/product/ERP5Type/Core/AcquiredProperty.py
@@ -131,10 +131,10 @@ class AcquiredProperty(StandardProperty):
         StandardProperty.exportToFilesystemDefinition(self)
 
     acquisition_portal_type_value = self._convertValueToTalesExpression(
-      self.getAcquisitionPortalType())
+      self.getAcquisitionPortalType()) or ()
 
     portal_type_value = self._convertValueToTalesExpression(
-      self.getContentPortalType())
+      self.getContentPortalType()) or ()
 
     filesystem_property_dict.update(
       {'acquisition_base_category': self.getAcquisitionBaseCategoryList(),