[WIP] Minor fixes

**do not merge yet WIP**

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| Refs tickets  | -
| License       | MIT
| Doc PR        | -
People might expect a string to be returned. I don't like this change, especially because the form framework is legacy, you should rather do 

    return new Response($form->execute())

in the controllers.