fields: fix support for optional fields using data sources with id/q (#35514)

tests/test_form_pages.py

@@ -5181,6 +5181,26 @@ remote.example.net = 1234
         assert formdef.data_class().select()[0].data['0_display'] == 'hello'
         assert formdef.data_class().select()[0].data['0_structured'] == data['data'][0]
 
+    # check with optional field
+    formdef.fields[0].required = False
+    formdef.store()
+
+    app = get_app(pub)
+    with mock.patch('qommon.misc.urlopen') as urlopen:
+        data = {'data': [{'id': '1', 'text': 'hello', 'extra': 'foo'},
+                         {'id': '2', 'text': 'world', 'extra': 'bar'}]}
+        urlopen.side_effect = lambda *args: StringIO.StringIO(json.dumps(data))
+        resp = app.get('/test/')
+        pq = resp.pyquery.remove_namespaces()
+        select2_url = pq('select').attr['data-select2-url']
+
+    resp = resp.form.submit('submit') # -> validation page
+    assert resp.form['f0'].value == ''
+    assert resp.form['f0_label'].value == ''
+
+    resp = resp.form.submit('submit') # -> submit
+    assert formdef.data_class().select()[0].data['0'] is None
+
 def test_item_field_autocomplete_jsonp_source(http_requests, pub):
     user = create_user(pub)
     formdef = create_formdef()

wcs/fields.py

@@ -1311,7 +1311,9 @@ class ItemField(WidgetField):
 
     def add_to_view_form(self, form, value = None):
         real_value = value
-        label_value = self.get_display_value(value)
+        label_value = ''
+        if value is not None:
+            label_value = self.get_display_value(value)
         self.field_key = 'f%s' % self.id
 
         get_request().form[self.field_key + '_label'] = label_value # :/