title: MongoDB projection ignores high level properties if nested one present
body: <p>My document structure is,</p>
  
  <pre><code>{
    _id: '',
    l1: {
      l21: {
        l31: ''
      },
      l22: {
        l32: ''
      }
    }
  }
  </code></pre>
  
  <p>When I do project like <code>{'l1.l21.l31': 1, 'l1': 1}</code>, only <code>l1.l21.l31</code> got projected. The second one <code>l1</code> is got ignored, ie <code>l22</code> is not getting projected. Is there a way to avoid this kind of situation? I have an API which generate project fields based on client request. So, I cannot ask client to include only high level property when coming to nested case. Can we include any switch or something to not ignore like the above one?</p>