I'm trying real-time trading.But there seems to be a slight problem.

[kemoduodejuxi]

code

    broker = bt.brokers.CCXTBroker(exchange='bitmex', currency='BTC/USD', config=broker_config)
    cerebro.setbroker(broker)

    hist_start_date = datetime.utcnow() - timedelta(minutes=1000)
    data = bt.feeds.CCXT(
        exchange='bitmex',
        symbol='BTC/USD',
        timeframe=bt.TimeFrame.Minutes,
        fromdate=hist_start_date,
        historical='True',
        compression = 5,
        )

It worked fine at first, but halfway through it, an error was reported.
out put：

2020-11-22, price, 18715.00
2020-11-22, price, 18696.00
2020-11-22, price, 18670.50
2020-11-22, price, 18604.50
2020-11-22, price, 18575.00
2020-11-22, price, 18605.50
Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\lib\site-packages\backtrader\stores\ccxtstore.py", line 122, in retry_method
    return method(self, *args, **kwargs)
  File "C:\ProgramData\Anaconda3\lib\site-packages\backtrader\stores\ccxtstore.py", line 144, in create_order
    amount=amount, price=price, params=params)
  File "C:\ProgramData\Anaconda3\lib\site-packages\ccxt\bitmex.py", line 1256, in create_order
    'ordType': self.capitalize(type),
  File "C:\ProgramData\Anaconda3\lib\site-packages\ccxt\base\exchange.py", line 788, in capitalize
    if len(string) > 1:
TypeError: object of type 'NoneType' has no len()

Is this a network issue or is bitmex not supported?
Thx.