Variable.py: fix variable guard expression.

product/ERP5Workflow/Document/Variable.py

@@ -78,7 +78,7 @@ class Variable(IdAsReferenceMixin("variable_", "prefix"), XMLObject):
           self.info_guard = Guard(permissions=self.getPermissionList(),
                         roles=self.getRoleList(),
                         groups=self.getGroupList(),
-                        expr=self.getExpression())
+                        expr=Expression(self.getExpression()))
 
         if self.getRoleList() is not None:
           self.info_guard.roles = self.getRoleList()