title: 'list' object has no attribute 'queryset' error when adding a autocomplete field to a model-form
body: <p>I want to add an another autocomplete field to my model.form.</p>
  
  <p>However, as soon as I add the autocomplete widget for the field "projektnummer" </p>
  
  <pre><code>'projektnummer': autocomplete.ModelSelect2(url='output:projekt-form-autocomplete'),
  </code></pre>
  
  <p>I get an wired template error I cannot make sense of. Do you have some ideas what I can do here?</p>
  
  <p>Thank you very much! :)</p>
  
  <p>error message:</p>
  
  <pre><code>AttributeError at /output/create/
  'list' object has no attribute 'queryset'
  Request Method: GET
  Request URL:    http://127.0.0.1:8000/output/create/
  Django Version: 1.8.7
  Exception Type: AttributeError
  Exception Value:    
  'list' object has no attribute 'queryset'
  
  Error during template rendering
  
  In template /home/bjoern/Developement/Django/Outputmeldetool/venv_outputmeldetool/lib/python3.5/site-packages/crispy_forms/templates/bootstrap3/field.html, error at line 28
  
  28 {% if field|is_checkbox and form_show_labels %}
  </code></pre>
  
  <p>forms.py</p>
  
  <pre><code>class KombiPublikationForm(forms.ModelForm):
  
      typtyp = forms.ModelChoiceField(label='Vorauswahl Outputtyp', required = False,
                                      queryset=KombiPublikationsTypTyp.objects.exclude(id__in=EXCLUDED_TYPTYP)
                                      )
  
      class Meta:
          model = KombiPublikation
          exclude = ['pub_sprache']
          widgets = {
              'freigabe': DateTimePicker(options={"format": "YYYY-MM-DD HH:mm", 'sideBySide': True}),
              'typid': autocomplete.ModelSelect2(url='output:typ-autocomplete', forward=['typtyp']),
  #adding following line generates the error:
              'projektnummer': autocomplete.ModelSelect2(url='output:projekt-form-autocomplete'),
              'monat': forms.NumberInput(),
          }
  
  
  
      def __init__(self, *args, **kwargs):
          super(KombiPublikationForm, self).__init__(*args, **kwargs)
  
          self.helper = FormHelper()
          self.helper.help_text_inline = True
          self.helper.form_tag = False
          self.helper.layout = Layout(
             #a lot of layout stuff is here
              )
  </code></pre>
  
  <p>edit:</p>
  
  <p>I get the very same error message with a reduced test form without crispy forms. Just the plain model-form and the one autocomplete widget. So it seems to be unreleated to crispy forms, but related to the autocomplete widget.</p>
  
  <pre><code>class TestPublikationForm(forms.ModelForm):
      class Meta:
          model = KombiPublikation
          exclude = ['pub_sprache']
          widgets = {
              'projektnummer': autocomplete.ModelSelect2(url='output:projekt-form-autocomplete'),
      }
  </code></pre>
  
  <p>template.html</p>
  
  <pre><code>{{ form }}
  </code></pre>
  
  <p>error:</p>
  
  <pre><code> Exception Value: 'list' object has no attribute 'queryset'
  </code></pre>