title: Swagger : nullable refs not in an array
body: <p>I'm using Swagger and I want to get with annotations an API doc like that :</p>
  <pre><code>&quot;myproperty&quot;:{
      &quot;nullable&quot;: true,
      &quot;$ref&quot;: &quot;#/components/schemas/MyProperty&quot;
  }
  </code></pre>
  <p>So I tried with :</p>
  <pre><code>  /**
     * @var MyProperty|null
     *
     * @OA\Schema(ref=@Model(type=MyProperty::class), nullable=true)
     */
    private $myproperty;
  </code></pre>
  <p>But when I generate my doc.json, I have :</p>
  <pre><code>&quot;myproperty&quot;: {
              &quot;nullable&quot;: true,
              &quot;allOf&quot;: [
                {
                  &quot;$ref&quot;: &quot;#/components/schemas/Meta&quot;
                }
              ]
            }
  </code></pre>
  <p>Having &quot;$ref&quot; in an array is an issue for me. How could I change that ?</p>