title: forms ModelChoiceField queryset + extra choice fields django forms
body: <p>I am trying to create a form in that ModelChoiceField loads from queryset and i want add few custom values to ModelChoiceField for extend i have used choice field, like below but while updating the form,getting below error</p>
  
  <p>Form Error :
  Select a valid choice. That choice is not one of the available choices.</p>
  
  <p>Code :</p>
  
  <pre><code> self.fields['lead'] = forms.ModelChoiceField(queryset = Pepole.objects.filter(poc__in       = ('lead','sr.lead')))
   self.fields['lead2'] = forms.ModelChoiceField(queryset = Pepole.objects.filter(role__in = ('lead','sr.lead')))
        choice_field = self.fields['lead']                                    
        choice_field.choices = list(choice_field.choices) + [('None', 'None')]
        choice_field = self.fields['lead2']                                    
        choice_field.choices = list(choice_field.choices) + [('None', 'None')]
  </code></pre>
  
  <p>Am i doing any thing wrong here?</p>