title: Nelmio 4 security definitions index not found
body: <p>I try to configure nelmio/api-doc-bundle to use Authorization header for my Bearer token.</p>
  <p>I configure it in <code>nelmio_api_doc.yaml</code> like this</p>
  <pre><code>nelmio_api_doc:
      documentation:
          info:
              title: title
              version: 1.0.0
          securityDefinitions:
              Bearer:
                  type: apiKey
                  description: 'jwt from oauth prefixed by `Bearer`'
                  name: Authorization
                  in: header
          security:
              -   Bearer: []
      areas: # to filter documented areas
          path_patterns:
              - ^/api(?!/doc$|/doc.json$) # Accepts routes under /api except /api/doc and /api/doc.json
  </code></pre>
  <p>But when i got to the ui doc page I got :</p>
  <p>Notice: Undefined index: securityDefinitions</p>
  <p>Did someone know how to fix it ?</p>