Using slugs with Django (Form + Model)

Question

I have the following error:

Error in page

Django admin DB

Shell object

The logic that I use in Django is based on a model and the ModelForm class. Here is the model:

from django.db import models
from django.core.validators import MinValueValidator, MaxValueValidator
from django.urls import reverse


class Ingredient(models.Model):
    name = models.CharField(max_length=100)


    def __str__(self):
        return f'{self.name}'


class Recipe(models.Model):
    slug = models.SlugField(null=True, unique=True, blank=True, editable=False)
    title = models.CharField(null=False, max_length=100)
    description = models.CharField(null=False, max_length=250)
    preparation = models.TextField(null=False)
    score = models.IntegerField(null=True, validators=[MinValueValidator(1), MaxValueValidator(5)])
    last_update = models.DateField(auto_now=True)
    presentation_image = models.ImageField(upload_to='images', null=True, blank=True)
    ingredients = models.ManyToManyField(Ingredient)


    def __str__(self):
        return f'{self.slug}, {self.title}, {self.description}, {self.preparation}, {self.score}, {self.last_update}, {self.presentation_image}, {self.ingredients}'

Here is the RecipeForm:

from django import forms
from django.core.validators import MinValueValidator, MaxValueValidator

from .models import Recipe
from .models import Ingredient


class RecipeForm(forms.ModelForm):
    class Meta:
        model = Recipe
        exclude = ['slug', 'last_update']
        widgets = {
            'preparation': forms.Textarea()
        }
        labels = {
            'title': 'Title',
            'description': 'Description',
            'preparation': 'Preparation',
            'score': 'Score',
            'presentation_image': 'Presentation Image',
            'ingredients': 'Ingredients'
        }

I understand that the problem is based on the fact that no slug is generated (since it is None in the shell). Since my path for a single recipe is based on a slug then Django simply tells me "Hey dude, no slug to work with, sorry... It's on you...".

This problem have occured when I tried to add a new recipe from the Django admin instead of my page (Here I can add the recipe but the slug will be None. In Django admin I just get the error)

What I can't understand is why the slug is not generated? The user must not enter a slug by it's own. It should be generated based on the title. User must not have a saying in it at the moment.

Can you please explain to me where my logic fails and what's the mistake so I can understand the issue clearly so I can avoid these rookie mistakes in the future?