python 爬虫tkinter模块报错object of type 'NoneType' has no len()

python 爬虫tkinter模块报错object of type 'NoneType' has no len()
代码：

import tkinter as tk
import train
from tkinter import ttk
from tkinter import messagebox,Label,Frame
import city

window = tk.Tk()

window.title("12306爬虫系统")
window.resizable(height=False,width=False)

window.geometry("800x450")


label1 = Label(window,text="出发地")
label2 = Label(window,text="目的地")
label3 = Label(window,text="出发时间")

e1 = tk.Entry(window, font=('Arial', 14))
e2 = tk.Entry(window, font=('Arial', 14))
e3 = tk.Entry(window, font=('Arial', 14))

label1.grid(row=0)
label2.grid(row=1)
label3.grid(row=2)

e1.grid(row=0,column=1,pady=5)
e2.grid(row=1,column=1,pady=5)
e3.grid(row=2,column=1,pady=5)



def deleleTree(tree):
    x = tree.get_children()
    for item in x:
        tree.delete(item)

def command():
    deleleTree(tree)
    from_station = e1.get().strip()
    to_station = e2.get().strip()
    if(city.getCityCode(from_station) is None):
        messagebox.askokcancel('提示', '出发地输入错误')
        return
    if(city.getCityCode(to_station) is None):
        messagebox.askokcancel('提示', '目的地输入错误')
        return
        
    train_date = e3.get().strip()
    trainList = []
    try:
        trainList = train.getAll(from_station,to_station,train_date)
    except Exception as e:
        messagebox.askokcancel("提示","查询超时，请稍后再试")
        raise e

    for i in range(0,len(trainList)):
       tree.insert("",i,values=trainList[i])

button = tk.Button(window,text='点我查询',command=command)
button.grid(row=3,column=9,pady=10)

tree = ttk.Treeview(window,show="headings")
tree['columns'] = ("车次","出发站","到达站","出发时间","到达时间","商务座","一等座","二等座","硬座","硬卧","软卧","无座")
width = 65
tree.column("车次",width=width)
tree.column("出发站",width=width)
tree.column("到达站",width=width)
tree.column("出发时间",width=width)
tree.column("到达时间",width=width)
tree.column("商务座",width=width)
tree.column("一等座",width=width)
tree.column("二等座",width=width)
tree.column("硬座",width=width)
tree.column("硬卧",width=width)
tree.column("软卧",width=width)
tree.column("无座",width=width)

for name in tree['columns']:
    tree.heading(name,text=name)

tree.grid(row=5,columnspan=10)

window.mainloop()

报错详细信息如图

train.getAll返回的是list类型吗？实际看一下trainList的类型。