title: How to set a Django filter to select all
body: <p>I have a view in Django that will read a get request and its parameters and make a query based on the parameters. Currently my view looks like this:</p>
  
  <pre><code>def getInventory(request):
      c = request.GET.get('category', '')
      g = request.GET.get('gender', '')
      s = request.GET.get('size', '')
  
      available = Item.objects.filter(gender=g,category=c,size=s)
      data = serializers.serialize('json',available)
      return HttpResponse(data,'json')
  </code></pre>
  
  <p>Sometimes, though, one of the parameters is not specified. I would like this to result in a value representing 'all' rather than an individual value. Is this possible in the way I've done it? I've tried <code>gender=None</code> but that just results in an empty list.</p>