'NoneType'对象没有属性'text'错误

Question

所以我使用xml将数据传输到我的数据库，4个表工作正常，但突然出现错误，我不知道如何解决它：

tables = soup.find_all('tabela_specjalnosci')

    # for each tabela_specjalnosci looks like there is 2 nested corresponding   tags
    tags = ['id', 'nazwa']
    # initialize empty dataframe
    df = pd.DataFrame()
    # iterate over each tabela_specjalnosci and extract each tag and append to pandas dataframe
    for table in tables:
        all = map(lambda x: table.find(x).text, tags) # everything fine
        df = df.append([all], ignore_index=True)
    # insert tags as columns
    df.columns = tags
    # add schedule row by row to database
    for row in df.iterrows():
        object = Specjalnosc(row[1])
        db.session.add(object)
        db.session.commit()

上面的代码工作正常，但下一个突然没有

tables = soup.find_all('tabela_studia')

    # for each tabela_studia looks like there is 2 nested corresponding   tags
    tags = ['id', 'nazwa']
    # initialize empty dataframe
    df = pd.DataFrame()
    # iterate over each tabela_studia and extract each tag and append to pandas dataframe
    for table in tables:
        all = map(lambda x: table.find(x).text, tags) #'NoneType' object has no attribute 'text'
        df = df.append([all], ignore_index=True)
    # insert tags as columns
    df.columns = tags
    # add schedule row by row to database
    for row in df.iterrows():
        object = Studia(row[1])
        db.session.add(object)
        db.session.commit()

我添加的xml如下所示：

<tabela_specjalnosci data-aktualizacji="1474562975">
  <ID>0</ID>
  <NAZWA><ogólna></NAZWA>
</tabela_specjalnosci>

和第二个：

<tabela_studia data-aktualizacji="1474563008">
  <ID>1</ID>
  <NAZWA>stac. magisterskie jednolite</NAZWA>
</tabela_studia>

这里有什么问题吗？