NOT NULL constraint failed: study_useranswer.email_id

Возникла проблема со связкой ответа и email, введенного пользователем.

views.py

def study(request, id):
quest1 = Quest.objects.get(pk = id)
a = Answer.objects.filter(quest = quest1)
ua = Useranswer()
if quest1.tip == '1':
    if request.method == "POST":
        if 'Назад'in request.POST:
            id = id-1
            return redirect('study', id)
        if "Вапросик" in request.POST:
            ua.quest = quest1
            ua.answer = request.POST["Вапросик"]
            ua.user = User.id
            ua.save()
        id += 1
        if id == 17:
            return redirect('study1')
        return redirect('study', id)
    else:
        return render(request, 'study/study_1.html', {'q': quest1, 'a': a})

models.py

class User(AbstractBaseUser):
    email = models.EmailField(
        verbose_name='email address',
        max_length=255,
        unique=True,
    )
    objects = UserManager()
    active = models.BooleanField(default=True)
    staff = models.BooleanField(default=False)
    admin = models.BooleanField(default=False)

    USERNAME_FIELD = 'email'
    REQUIRED_FIELDS = []

    def get_full_name(self):
        return self.email

    def get_short_name(self):
        return self.email

    def __str__(self):
        return self.email

    def has_perm(self, perm, obj=None):
        "Does the user have a specific permission?"
        return True

    def has_module_perms(self, app_label):
        "Does the user have permissions to view the app `app_label`?"
        return True

    @property
    def is_staff(self):
        return self.staff

    @property
    def is_admin(self):
        "Is the user a admin member?"
        return self.admin

    @property
    def is_active(self):
        return self.active
        "Is the user active?"


class Useranswer(models.Model):
    answer = models.CharField(max_length=200)
    email = models.ForeignKey('User', on_delete=models.CASCADE)
    quest = models.ForeignKey('Quest', on_delete=models.CASCADE,)

    def __str__(self):
        return self.answer
        return self.email

forms.py

class RegisterForm(forms.ModelForm):
    password = forms.CharField(widget=forms.PasswordInput)
    password2 = forms.CharField(label='Confirm password', widget=forms.PasswordInput)

    class Meta:
        model = User
        fields = ('email',)

    def clean_email(self):
        email = self.cleaned_data.get('email')
        qs = User.objects.filter(email=email)
        if qs.exists():
            raise forms.ValidationError("email is taken")
        return email

    def clean_password2(self):
        # Check that the two password entries match
        password1 = self.cleaned_data.get("password1")
        password2 = self.cleaned_data.get("password2")
        if password1 and password2 and password1 != password2:
            raise forms.ValidationError("Passwords don't match")
        return password2


class UserAdminCreationForm(forms.ModelForm):
    """
    A form for creating new users. Includes all the required
    fields, plus a repeated password.
    """
    password1 = forms.CharField(label='Password', widget=forms.PasswordInput)
    password2 = forms.CharField(label='Password confirmation', widget=forms.PasswordInput)

    class Meta:
        model = User
        fields = ('email',)

    def clean_password2(self):
        # Check that the two password entries match
        password1 = self.cleaned_data.get("password1")
        password2 = self.cleaned_data.get("password2")
        if password1 and password2 and password1 != password2:
            raise forms.ValidationError("Passwords don't match")
        return password2

    def save(self, commit=True):
        # Save the provided password in hashed format
        user = super(UserAdminCreationForm, self).save(commit=False)
        user.set_password(self.cleaned_data["password1"])
        if commit:
            user.save()
        return user


class UserAdminChangeForm(forms.ModelForm):
    """A form for updating users. Includes all the fields on
    the user, but replaces the password field with admin's
    password hash display field.
    """
    password = ReadOnlyPasswordHashField()

    class Meta:
        model = User
        fields = ('email', 'password', 'active', 'admin')

    def clean_password(self):
        return self.initial["password"]