title: Mongoengine PointField gives location object expected, location array not in correct format error
body: <p>I have a model as follows:</p>
  
  <pre><code>class Station(Document):
      location = PointField()
  </code></pre>
  
  <p>Trying to write data as follows:</p>
  
  <pre><code>station = Station()
  station.location = {
      "type": "Point",
      "coordinates": [
        81.4471435546875,
        23.61432859499169
      ]
    }
  station.save()
  </code></pre>
  
  <p>However this gives the error <code>Could not save document (location object expected, location array not in correct format)</code></p>
  
  <p>Mongoengine documentation says such a dictionary should be OK. What am I missing here? </p>