ModelChoiceField gives "Select a valid choice" error on submission
<p>Here is my simple form with one <code>ModelChoiceField</code>:</p>

<pre><code>class PropertyFilter(forms.Form):
    type = forms.ModelChoiceField(queryset=Property.objects.order_by().values_list('type', flat=True).distinct(),
                                  empty_label=None)
</code></pre>

<p>It allows user to choose from one of the options (each represented as a string). When i choose an option and hit "Submit" - it returns:</p>

<blockquote>
  <p>Select a valid choice. That choice is not one of the available
  choices.</p>
</blockquote>

<p>My <code>views.py</code> looks like this:</p>

<pre><code>from models import Property
from .forms import PropertyFilter

def index(request):
    if request.method == 'POST':
        form = PropertyFilter(request.POST)
        if form.is_valid():
            return HttpResponseRedirect('/')
    else:
        form = PropertyFilter()
        properties = Property.objects.all()
    return render(request, 'index.html',  context=locals())
</code></pre>

<p>What am i doing wrong?</p>