def METHOD_NAME(self):
    user = self.cleaned_data['user'].lower()
    if user:
        # if Django User object exists return it, otherwise create one
        try:
            user_obj = User.objects.get(username__iexact=user)
        except User.DoesNotExist:
            user_obj = User.objects.create_user(username=user, email=user)
        return user_obj
    else:
        return None