請問為什么運行下載代碼的程序時，會出現(xiàn)這樣的情況呢：

Traceback (most recent call last):

? File "C:\Users\yuanqi\Desktop\dangdang.py", line 102, in <module>

? ? main()

? File "C:\Users\yuanqi\Desktop\dangdang.py", line 97, in main

? ? result = d.parse_item(items=items)

? File "C:\Users\yuanqi\Desktop\dangdang.py", line 50, in parse_item

? ? for item in items:

TypeError: 'NoneType' object is not iterable