Fix workflow bug "Local variable 'value' referenced before assignment"

See merge request nexedi/erp5!1704

bt5/erp5_core_test/TestTemplateItem/portal_components/test.erp5.testERP5Workflow.py

@@ -131,6 +131,22 @@ class TestERP5Workflow(ERP5TypeTestCase):
 
     history = doc.workflow_history['wf']
     self.assertEqual(len(history), 2)# create, transition1
+    
+    transition_variable = transition1.newContent(
+      portal_type='Workflow Transition Variable',
+      causality_value=variable1,
+      variable_default_expression='string:Set by transition variable',
+    )
+    workflow._executeTransition(doc,transition1)
+    self.assertEqual(
+      workflow.getCurrentStatusDict(doc)['variable1'],
+      "Set by transition variable")
+
+    # Without an expression, the variable is set to None
+    transition_variable.setVariableDefaultExpression(None)
+    workflow._executeTransition(doc,transition1)
+    self.assertEqual(workflow.getCurrentStatusDict(doc)['variable1'], None)
+
 
 
   def test_afterScript(self):

product/ERP5Type/Core/Workflow.py

@@ -860,6 +860,7 @@ class Workflow(XMLObject):
         continue
 
       expr = None
+      value = None
       if variable_id in transition_expression_dict:
         expr = transition_expression_dict[variable_id]
       elif not vdef.getAutomaticUpdate() and variable_reference in former_status: