AttributeError: 'NoneType' object has no attribute 'find_all' Beautifulsoup

I'm trying to scrape a house's price of this link : https://www.leboncoin.fr/ventes_immobilieres/offres/ile_de_france/p-2/

And I need to know what wrong with my program ?

My program :

import csv
import requests
from bs4 import BeautifulSoup

with open("bc.csv", "w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["prix", "code_postal", "description", "nombre_pieces", "surface"]) 
    for i in range(1, 20):
        url = "https://www.leboncoin.fr/ventes_immobilieres/offres/ile_de_france/p-%s/" % i
        soup = BeautifulSoup(requests.get(url).text, "html.parser")
        repo = soup.find(class_="undefined")
        for repo in repo.find_all("li", attrs={"itemscope itemtype": "http://schema.org/Offer"}):
            prix = repo.find("span", {"itemprop": "priceCurrency"})
            prix = prix.text if prix else ""
            writer.writerow([prix])

I get this error :

Traceback (most recent call last):
File "nv.py", line 14, in <module>
for repo in repo.find_all("li", attrs={"itemscope itemtype": "http://schema.org/Offer"}):
AttributeError: 'NoneType' object has no attribute 'find_all'