python - AttributeError の奇妙なエラー: 'NoneType' オブジェクトに属性 'getText' がありません

Question

import os, re, sys, urllib2
from bs4 import BeautifulSoup
import lxml

def get_epg(channel, html):
    soup = BeautifulSoup(html, "lxml")
    main_div = soup.find("div", {"class":"viewport-container"})
    elements = main_div.find_all("li")
    for element in elements:
        cmp = element.find("div", { "class" : "channel" } ).getText()
        #return cmp
        if channel == cmp:
            print "found"
            return element

EPG_URL = "http://www.hoerzu.de/tv-programm/jetzt/"
html = urllib2.urlopen(EPG_URL)
print get_epg("ZDF", html)

結果:

Traceback (most recent call last):
  File "epg.py", line 17, in <module>
    print get_epg("ZDF", html)
  File "epg.py", line 10, in get_epg
    cmp = element.find("div", { "class" : "channel" } ).getText()
AttributeError: 'NoneType' object has no attribute 'getText'

ここで何が悪いのか本当にわかりません。

    for element in elements:
        cmp = element.find("div", { "class" : "channel" } ).getText()
        return cmp

エラーは表示されず、すべてが期待どおりに進みます...