exportToFilesystemDefinition returns None if the reference is None,

thus add a check in AcquiredProperty



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@43650 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5Type/Core/AcquiredProperty.py

@@ -130,6 +130,9 @@ class AcquiredProperty(StandardProperty):
     filesystem_property_dict = \
         StandardProperty.exportToFilesystemDefinition(self)
 
+    if filesystem_property_dict is None:
+      return None
+
     acquisition_portal_type_value = self._getExpressionFromString(
       self.getAcquisitionPortalType())