workflows: don't crash on display form action with undefined form (#49187)

tests/form_pages/test_all.py

@@ -4450,6 +4450,47 @@ def test_formdata_generated_document_in_private_history(pub):
     assert 'Form exported in a model' in resp.text
 
 
+def test_formdata_empty_form_action(pub):
+    create_user(pub)
+    wf = Workflow(name='status')
+    st1 = wf.add_status('Status1', 'st1')
+    wf.add_status('Status2', 'st2')
+
+    display_form = FormWorkflowStatusItem()
+    display_form.id = '_x'
+    display_form.by = ['_submitter']
+    display_form.varname = 'xxx'
+    st1.items.append(display_form)
+    display_form.parent = st1
+
+    jump1 = ChoiceWorkflowStatusItem()
+    jump1.id = '_jump1'
+    jump1.label = 'Jump 1'
+    jump1.by = ['_submitter']
+    jump1.status = 'st2'
+    jump1.parent = st1
+    st1.items.append(jump1)
+
+    wf.store()
+
+    formdef = create_formdef()
+    formdef.workflow_id = wf.id
+    formdef.fields = []
+    formdef.store()
+    formdef.data_class().wipe()
+
+    resp = login(get_app(pub), username='foo', password='foo').get('/test/')
+    resp = resp.forms[0].submit('submit')
+    assert 'Check values then click submit.' in resp.text
+    resp = resp.forms[0].submit('submit')
+    assert resp.status_int == 302
+    resp = resp.follow()
+    assert 'The form has been recorded' in resp.text
+
+    resp = resp.form.submit('button_jump1')
+    assert formdef.data_class().select()[0].status == 'wf-st2'
+
+
 def test_formdata_form_file_download(pub):
     create_user(pub)
     wf = Workflow(name='status')

wcs/wf/form.py

@@ -191,6 +191,8 @@ class FormWorkflowStatusItem(WorkflowStatusItem):
         FormPage.apply_field_prefills({}, form, fields)
 
     def evaluate_live_form(self, form, formdata, user):
+        if not self.formdef:
+            return
         workflow_data = {}
         for k, v in get_dict_with_varnames(
                         self.formdef.fields, self.formdef.get_data(form),