title: xml to yaml: You cannot define a sequence item when in a mapping in
body: <p>can anybody tell me what's the problem in converting the xml to yaml?(i've tried to do it but i get an error that says "You cannot define a sequence item when in a mapping in ")</p>
  
  <pre><code>&lt;service id="sonata.news.admin.post" class="%sonata.news.admin.post.class%"&gt;
      &lt;tag name="sonata.admin" manager_type="orm" group="sonata_blog" label="post"/&gt;
      &lt;argument /&gt;
      &lt;argument&gt;%sonata.news.admin.post.entity%&lt;/argument&gt;
      &lt;argument&gt;%sonata.news.admin.post.controller%&lt;/argument&gt;
  
      &lt;call method="setUserManager"&gt;
          &lt;argument type="service" id="fos_user.user_manager" /&gt;
      &lt;/call&gt;
  
  &lt;/service&gt;
  </code></pre>
  
  <p>and converted yaml file:</p>
  
  <pre><code>sonata.news.admin.post:
      class: "%sonata.news.admin.post.class%"
      arguments: [%sonata.news.admin.post.entity%]
      arguments: [%sonata.news.admin.post.controller%]
      tags:
          - { name: sonata.admin, manager_type: orm, group: sonata_blog, label: post}
      call:
          - {method: setUserManager}
          service:
              fos_user.user_manager
  </code></pre>