Как делать цепочки диалогов в Telegram Bot?

2019-01-13 19:29:22,752 (util.py:64 WorkerThread2) ERROR - TeleBot: "TypeError occurred, args=("'NoneType' object is not callable",)
Traceback (most recent call last):
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\telebot\util.py", line 58, in run
    task(*args, **kwargs)
TypeError: 'NoneType' object is not callable
"
Traceback (most recent call last):
  File "C:\Users\Rizvan\Desktop\Telegram Bot\bot.py", line 93, in <module>
    bot.polling(none_stop=True)
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\telebot\__init__.py", line 264, in polling
    self.__threaded_polling(none_stop, interval, timeout)
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\telebot\__init__.py", line 288, in __threaded_polling
    self.worker_pool.raise_exceptions()
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\telebot\util.py", line 107, in raise_exceptions
    six.reraise(self.exc_info[0], self.exc_info[1], self.exc_info[2])
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\six.py", line 693, in reraise
    raise value
  File "C:\Users\Rizvan\Desktop\Telegram Bot\venvbot\lib\site-packages\telebot\util.py", line 58, in run
    task(*args, **kwargs)
TypeError: 'NoneType' object is not callable
[Finished in 11.6s]

import telebot
from telebot import types
import json
from models import *

token = 'мой токен'
bot = telebot.TeleBot(token)


@bot.message_handler(commands=['start'])
def start(message):
	 
	markup = types.ReplyKeyboardMarkup(one_time_keyboard=True)
	markup.row('Сформировать заказ')
	
	
	msg = bot.send_message(message.chat.id,'Выберите вариант',reply_markup=markup)
	bot.register_next_step_handler(msg, user_enter)

@bot.message_handler(regexp='сформировать заказ')
def user_enter(message):
	if message.text.lower() == 'сформировать заказ':
		catalog = session.query(Catalog).all()
		markup = types.ReplyKeyboardMarkup()
		for product in catalog:
			markup.row(product.name)
		msg = bot.send_message(message.chat.id,'Выберите товар', reply_markup=markup)
		bot.register_next_step_handler(msg, user_choice)



def user_choice(message):
	catalog = session.query(Catalog).all()
	markup = types.ReplyKeyboardMarkup()

	for product in catalog:
		if product.name == message.text :
	
			msg = bot.send_message(message.chat.id, 'Введите количество')
			
			bot.register_next_step_handler(msg,product_count(message=message,product=product))


def product_count(message, product):
	
	count = message.text

	msg = bot.send_message(message.chat.id, 'Товар добавлен в корзину , вы можете продолжить покупки или сделать заказ')
	bot.register_next_step_handler(msg, add_to_basket(message,product,count))



def add_to_basket(message,product,count):
	prod = Basket(message.from_user.id)
	prod.prods.append(product)
	session.add(prod)
	session.commit()
	user_enter(message)

if __name__ == '__main__':
	bot.polling(none_stop=True)