workflows: properly import/export hidden comment button label (#5208)

tests/test_workflow_import.py

@@ -177,3 +177,18 @@ def test_jump_action():
     assert wf2.possible_status[0].items[0].condition == '"foo"'
     assert wf2.possible_status[0].items[0].trigger == 'bar'
     assert wf2.possible_status[0].items[0].timeout == 1200
+
+
+def test_commentable_action():
+    wf = Workflow(name='status')
+    st1 = wf.add_status('Status1', 'st1')
+
+    commentable = CommentableWorkflowStatusItem()
+    commentable.id = '_commentable'
+    commentable.by = ['_submitter', '_receiver']
+    commentable.button_label = None
+    st1.items.append(commentable)
+    commentable.parent = st1
+
+    wf2 = assert_import_export_works(wf)
+    assert wf2.possible_status[0].items[0].button_label is None

wcs/workflows.py

@@ -977,6 +977,8 @@ class CommentableWorkflowStatusItem(WorkflowStatusItem):
         if self.button_label == 0:
             pass
         elif self.button_label is None:
+            # button_label being None is a special case meaning "no button", it
+            # should be handled differently than the "not filled" case
             el = ET.SubElement(xml_item, 'button_label')
         else:
             el = ET.SubElement(xml_item, 'button_label')
@@ -988,9 +990,14 @@ class CommentableWorkflowStatusItem(WorkflowStatusItem):
                 raise AssertionError('unknown type for button_label (%r)' % self.button_label)
 
     def button_label_init_with_xml(self, element, charset):
-        if element is None or element.text is None:
+        if element is None:
             return
-        self.button_label = element.text.encode(charset)
+        if element.text is None:
+            # this means element is self-closing, <button_label />, which maps
+            # to None, meaning "no button".
+            self.button_label = None
+        else:
+            self.button_label = element.text.encode(charset)
 
 register_item_class(CommentableWorkflowStatusItem)