title: CastError in mongoDB nearSphere method in mongoose 3.8.3
body: <p>I use in mongoose version 3.8.3 the mongoDB $nearSphere method to find nearby locations.</p>
  
  <pre><code>mongoose.models['Event']
          .find({ loc : 
                  { 
                      $nearSphere : 
                      { 
                          $geometry : loc,
                          $maxDistance : 100000
                      }
                  }           
           })
          .limit(100)
          .exec(function (err, events)
          {
              console.log(err)
              ...
          }
  </code></pre>
  
  <p>The loc field in the Events Scheme has a '2dsphere' index:</p>
  
  <pre><code>var EventSchema = new Schema
  ({  
      ...
      loc: 
      {
          type: { type: String },
          coordinates: { type: [Number], index: '2dsphere' }
      },
      ...
  });
  </code></pre>
  
  <p>The variable loc is of type 'Point'. An example is:</p>
  
  <pre><code>{ coordinates: [ 12.93598683338508, 48.43299197266921 ], type: 'Point' }
  </code></pre>
  
  <p>After executing the above search statement I always get the error:</p>
  
  <pre><code>2013-12-27T08:46:57.997102+00:00 app[web.1]: { message: 'Cast to number failed for value "Point" at path "__QueryCasting__"',
  2013-12-27T08:46:57.997105+00:00 app[web.1]:   name: 'CastError',
  2013-12-27T08:46:57.997107+00:00 app[web.1]:   type: 'number',
  2013-12-27T08:46:57.997108+00:00 app[web.1]:   value: 'Point',
  2013-12-27T08:46:57.997110+00:00 app[web.1]:   path: '__QueryCasting__' }
  </code></pre>
  
  <p>Can somebody figure out why this error appears and how to solve it?</p>