if no value is set on the Acquired Property for portal types, a TUPLE should be returned

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@42851 20353a03-c40f-0410-a6d1-a30d3c3de9de

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(),