Not able to pass logical answer received from Form to NullBoolean model

My model is like

 class mymodel(models.Model):
      param1=models.NullBooleanField(blank=False)

My form is

class MyForm01(forms.Form):
    LCHOICES=[(True, 'Yes'),(False,'No')]
    answer=forms.ChoiceField(
    label='Question', 
    choices=LCHOICES, 
    widget=forms.RadioSelect(),
    help_text='Help text')

I am trying to pass the user choice to a model for saving as below, where id_number is a new number for new object creation.

 myobj=mymodel.objects.create(
        id=mymodel.objects.get(id=id_number),             
        param1=form.cleaned_data.['answer']
        )

Everything happens, including new object creation but the data passed is always True even when the original answer is negative. If I take a print of answer its coming as False. Also if I change form.cleaned_data.['answer'] to False, it is well accepted.

Where am I making a mistake?