Как исправить ошибку NOT NULL constraint failed?

models.py

from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=20)

    def __str__(self):
        return self.name

class Type(models.Model):
    product_type = models.ForeignKey(Product, on_delete=models.CASCADE)
    text = models.TextField()

    class Meta:
        verbose_name_plural = 'types'

    def __str__(self):
        if len(self.text) > 50:
            return self.text[:50] + "..."
        else:
            return self.text

forms.py

from django import forms
from .models import Product, Type

class ProductForm(forms.ModelForm):
    class Meta:
        model = Product
        fields = ['name']
        labels = {'name': ''}

class TypeForm(forms.ModelForm):
    class Meta:
        model = Type
        fields = ['text']
        labels = {'text': ''}
        widgets = {'text': forms.Textarea(attrs={'cols': 80})}

файл views.py (проблемная зона)

def new_type(request, product_id):
    product = Product.objects.get(id=product_id)
    if request.method != 'POST':
        form = TypeForm()
    else:
        form = TypeForm(data=request.POST)
        if form.is_valid():
            new_receipt = form.save(commit=False)
            new_receipt.product = product
            new_receipt.save()
            return HttpResponseRedirect(reverse('vitamin_pluss:product_type', args=[product_id]))

    context = {'product': product, 'form': form}
    return render(request, 'vitamin_pluss/new_type.html', context)

Сообщение об ошибке

NOT NULL constraint failed: vitamin_pluss_type.product_type_id
Request Method: POST
Request URL:    http://localhost:8000/new_type/4/
Django Version: 2.2.2
Exception Type: IntegrityError
Exception Value:    
NOT NULL constraint failed: vitamin_pluss_type.product_type_id
Exception Location: C:\Users\Рома\AppData\Local\Programs\Python\Python37\lib\site-packages\django\db\backends\sqlite3\base.py in execute, line 383
Python Executable:  C:\Users\Рома\AppData\Local\Programs\Python\Python37\python.exe
Python Version: 3.7.0
d:\python_work\python_project\vitamin_plus\vitamin_pluss\views.py in new_type
            new_receipt.save() …
▼ Local vars
Variable    Value
form    
<TypeForm bound=True, valid=True, fields=(text)>
new_receipt 
<Type: hhhh>
product 
<Product: Chicken>
product_id  
4
request 
<WSGIRequest: POST '/new_type/4/'>