title: Geodjango GeoJSON Serializer geometry always 'null'
body: <p>Hello friends of GeoDjango and the GeoJSON serlizer. I was following the official GeoDjango Tutorial:
  <a href="https://docs.djangoproject.com/en/1.8/ref/contrib/gis/tutorial/" rel="nofollow">https://docs.djangoproject.com/en/1.8/ref/contrib/gis/tutorial/</a></p>
  
  <p>So in the end I have a PostgreSQL + PostGIS database full of countries of, their <code>name</code>, their <code>iso3</code> code and so on. And especially their geometry in <code>mpoly</code> as MultiPolygon (stored in wkb). I want to retrieve the contries from the database using GeoDjango. I am truggling with that.</p>
  
  <p>I can retrieve the properties of one object one after the other:</p>
  
  <pre><code>from django.http import HttpResponse
  from django.shortcuts import render
  from django.core.serializers import serialize
  from AppName.models import WorldBorder
  
  [...]
  
  WorldBorder.objects.filter(name='Germany')[0].name           # "Germany"
  WorldBorder.objects.filter(name='Germany')[0].iso3           # "DEU"
  WorldBorder.objects.filter(name='Germany')[0].mpoly.geojson  # long &amp; correct output
  </code></pre>
  
  <p>So the data is correctly stored in the database and I can retrieve the objects properties. Now I want to get a full geojson file for the country. Django has created the GeoJSON serializer for that:
  <a href="https://docs.djangoproject.com/en/1.8/ref/contrib/gis/serializers/" rel="nofollow">https://docs.djangoproject.com/en/1.8/ref/contrib/gis/serializers/</a></p>
  
  <p>If I use it in the described way:</p>
  
  <pre><code>serialize('geojson',
    WorldBorder.objects.filter(name='Germany'),
    geometry_field='mpoly',
    fields=('name',)
  )
  </code></pre>
  
  <p>I get this output:</p>
  
  <pre><code>u'{"type": "FeatureCollection", "crs":{"type": "name", "properties": {"name": "EPSG:4326"}},
      "features": [{"geometry": null,"type": "Feature",
      "properties":{"name": "Germany" }}]}'
  </code></pre>
  
  <p>what is driving me crazy is <code>"geometry": null</code></p>
  
  <p>So it serializes everything, but not the geometry. Why is that? What am I doing wrong? And especially? How do I get the geometry out of my PostGIS database in GeoJSON format using GeoDjango? Any help is appreciated.</p>
  
  <p>Thank you :)</p>