title: Getting returns an invalid response type for an http request error in odoo15
body: <p>I'm encountering an error like this while I try to fetch some data in odoo 15</p>
  <pre><code>odoo.http: &lt;function odoo.addons.vehicle_management.controllers.main.vehicle_web_form&gt;returns an invalid response type for an http request
  </code></pre>
  <p>Here is my python code</p>
  <pre><code>@http.route('/vehicle_web_form', methods=['GET'],  website=True, auth='public', csrf=False)
  def vehicle_web_form(self, **kw):
      print(kw)
      id = kw.get(&quot;id&quot;)
      print(id)
      print(type(id))
      return id
  </code></pre>