为什么此代码给我一个Nonetype错误代码

Question

对于学校，我需要创建一个服务器端登录页面，现在的问题是我在WSGI代码中不断收到NoneType错误代码，我认为这与查询中的内容有关，但我不确定

def application(environ,start_response):
    status = '200 OK'
    response_header = [('Content-type', 'text/html')]
    start_response(status, response_header)

    method = environ.get('REQUEST_METHOD', '')

    params = {}
    if method == 'GET':
        params = urlparse.parse_qs(environ['QUERY_STRING'])
    elif method == 'POST':
        input = environ['wsgi.input'].read().decode()
        params = urlparse.parse_qs(input)

        achternaam = params.get('achterNaam', [''])[0]
        ticketnummer = params.get('ticketNummer', [''])[0]
        db_query(achternaam,ticketnummer)

def login(fetch,achternaam,ticketnummer):
        if achternaam == fetch[0] and ticketnummer == fetch[1]:
            somethingtodo
        else:
            somethingelsetodo
def db_query(achternaam,ticketnummer):
    fetch = []
    fysdb = mysql.connect(
        host='localhost',
        database='FYS',
        user='admin',
        passwd='admin'
    )
    cursor = fysdb.cursor()
    query = "SELECT lastname, ticketnumber FROM passenger WHERE lastname = %s AND ticketnumber = %s"
    cursor.execute(query, (achternaam,ticketnummer))
    fetch = cursor.fetchall()
    fysdb.close()
    login(fetch,achternaam,ticketnummer)


#db_query(achternaam,ticketnummer)```