workflows: set bo fields to empty value only if value before compute is empty (#45135)

tests/test_workflows.py

@@ -3784,6 +3784,16 @@ def test_set_backoffice_field(http_requests, two_pubs):
     formdata = formdef.data_class().get(formdata.id)
     assert formdata.data['bo1'] is None
 
+    # check a value computed as the empty string is stored as an empty string, not None
+    item.fields = [{'field_id': 'bo1', 'value': '=""'}]
+    item.perform(formdata)
+    formdata = formdef.data_class().get(formdata.id)
+    assert formdata.data['bo1'] == ''
+    item.fields = [{'field_id': 'bo1', 'value': '{{ does_not_exist }}'}]
+    item.perform(formdata)
+    formdata = formdef.data_class().get(formdata.id)
+    assert formdata.data['bo1'] == ''
+
     assert LoggedError.count() == 0
 
     item.fields = [{'field_id': 'bo1', 'value': '= ~ invalid python ~'}]
@@ -4233,7 +4243,7 @@ def test_set_backoffice_field_date(two_pubs):
 
     # invalid values => do nothing
     assert LoggedError.count() == 0
-    for value in ('plop', {}, []):
+    for value in ('plop', '={}', '=[]'):
         item = SetBackofficeFieldsWorkflowStatusItem()
         item.parent = st1
         item.fields = [{'field_id': 'bo1', 'value': value}]

wcs/wf/backoffice_fields.py

@@ -107,16 +107,15 @@ class SetBackofficeFieldsWorkflowStatusItem(WorkflowStatusItem):
             except IndexError:
                 continue
 
-            try:
-                new_value = self.compute(field['value'], raises=True,
-                                         formdata=formdata, status_item=self)
-            except:
-                continue
-
-            if new_value == '':
-                # assign empty strings as None, as that will work for all field
-                # types
+            if not field.get('value'):
+                # assign empty value as None, as that will work for all field types
                 new_value = None
+            else:
+                try:
+                    new_value = self.compute(field['value'], raises=True,
+                                             formdata=formdata, status_item=self)
+                except:
+                    continue
 
             if formdef_field.convert_value_from_anything:
                 try: