Website form delivers an email with "undefined" title

If you receive an email from a form on the website, that has a title of "undefined", then you need to go to the form and perform the following steps:

1. Go to the page where the form is located and click on the page title.
2. Click on the form block inside the page, so that its settings appear on the right.
3. Under properties, expand the area "Labels and texts"
4. Find the field "Title" and add a message to identify the form
5. Click on Save, top right, to save the changes. Then refresh or reload the page.
6. Test in the frontend