How to check many variables in Python if not null?

I'm writing a python scraper code for OpenData and I have one question about : how to check if all values aren't filled in site and if it is null change value to null.

My scraper is here : http://ift.tt/1IRGoaj

Currently I'm working on it to optimalize.

My variables now look like:

    evcisloval = soup.find_all('td')[3].text.strip()
    prinalezival = soup.find_all('td')[5].text.strip()
    popisfaplnenia = soup.find_all('td')[7].text.replace('\"', '')
    hodnotafaplnenia = soup.find_all('td')[9].text[:-1].replace(",", ".").replace(" ", "")
    datumdfa = soup.find_all('td')[11].text
    datumzfa = soup.find_all('td')[13].text
    formazaplatenia = soup.find_all('td')[15].text
    obchmenonazov = soup.find_all('td')[17].text
    sidlofirmy = soup.find_all('td')[19].text
    pravnaforma = soup.find_all('td')[21].text
    sudregistracie = soup.find_all('td')[23].text
    ico = soup.find_all('td')[25].text
    dic = soup.find_all('td')[27].text
    cislouctu = soup.find_all('td')[29].text

And Output :

scraperwiki.sqlite.save(unique_keys=["invoice_id"],
                                    data={  "invoice_id":number,
                                            "invoice_price":hodnotafaplnenia,
                                            "evidence_no":evcisloval,
                                            "paired_with":prinalezival,
                                            "invoice_desc":popisfaplnenia,
                                            "date_received":datumdfa,
                                            "date_payment":datumzfa,
                                            "pay_form":formazaplatenia,
                                            "trade_name":obchmenonazov,
                                            "trade_form":pravnaforma,
                                            "company_location":sidlofirmy,
                                            "court":sudregistracie,
                                            "ico":ico,
                                            "dic":dic,
                                            "accout_no":cislouctu,
                                            "invoice_attachment":urlfa,
                                            "invoice_url":url})

I googled it but without success.