Incompatible with optstrategy?

[tsuga]

I run into an error when developing my bot.
This is the minimum code that reproduce the error.

Could you help me?

import time
from datetime import datetime

import backtrader as bt

from ccxtbt import CCXTFeed


def main():
    class TestStrategy(bt.Strategy):
        params = (
            ('maperiod', 10),
        )

        def __init__(self):
            self.next_runs = 0

        def next(self, dt=None):
            dt = dt or self.datas[0].datetime.datetime(0)
            print('%s closing price: %s' % (dt.isoformat(), self.datas[0].close[0]))
            self.next_runs += 1

    cerebro = bt.Cerebro()

    # cerebro.addstrategy(TestStrategy)
    cerebro.optstrategy(TestStrategy, maperiod=[10,11], printlog=True)

    # Add the feed
    cerebro.adddata(CCXTFeed(exchange='binance',
                             dataname='BNB/USDT',
                             timeframe=bt.TimeFrame.Minutes,
                             fromdate=datetime(2019, 1, 1, 0, 0),
                             todate=datetime(2019, 1, 1, 0, 2),
                             compression=1,
                             ohlcv_limit=2,
                             currency='BNB',
                             retries=5,
                            config={'enableRateLimit': True, 'nonce': lambda: str(int(time.time() * 1000))}))

    # Run the strategy
    cerebro.run(maxcups=1)


if __name__ == '__main__':
    main()

Error

Traceback (most recent call last):
  File "PATH_TO_CODE/sam-app/app/btccxt.py", line 45, in <module>
    main()
  File "PATH_TO_CODE/sam-app/app/btccxt.py", line 41, in main
    cerebro.run(maxcups=1)
  File "PATH_TO_CODE\venv\lib\site-packages\backtrader\cerebro.py", line 1143, in run
    for r in pool.imap(self, iterstrats):
  File "PATH_TO_PYTHON\lib\multiprocessing\pool.py", line 748, in next
    raise value
  File "PATH_TO_PYTHON\lib\multiprocessing\pool.py", line 431, in _handle_tasks
    put(task)
  File "PATH_TO_PYTHON\lib\multiprocessing\connection.py", line 206, in send
    self._send_bytes(_ForkingPickler.dumps(obj))
  File "PATH_TO_PYTHON\lib\multiprocessing\reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
AttributeError: Can't pickle local object 'main.<locals>.<lambda>'