ERP5Workflow: fix performance issue

product/ERP5Workflow/Document/Workflow.py

@@ -701,8 +701,9 @@ class Workflow(IdAsReferenceMixin("", "prefix"), XMLObject):
         # Preserve former value
         value = former_status[variable_reference]
       else:
-        if vdef.getVariableExpression() is not None:
-          expr = vdef.getVariableExpression()
+        variable_expression = vdef.getVariableExpression()
+        if variable_expression is not None:
+          expr = variable_expression
         else:
           value = vdef.getVariableValue(object=object)
       if expr is not None and expr != '':