btoandav20: Trailing Stop by percent gives error

Using trailamount seems to be ok, but trailpercent gives error.

self.long_order2 = self.buy_bracket(exectype=bt.Order.Stop, stopexec=bt.Order.StopTrail, size=qty,
            limitprice=TP2_price,
            
            price=entry_price,
            
            # stopprice=stoploss_price,
            stopargs={
                # 'trailamount': stop_dist,
                'trailpercent': 0.01,
            },
        )

  File "brokers/backtrader/algo.py, line 574, in buy_risk
    'trailpercent': 0.01,
  File "/usr/local/lib/python3.7/site-packages/backtrader/strategy.py", line 1169, in buy_bracket
    olimit = self.sell(**kargs)
  File "/usr/local/lib/python3.7/site-packages/backtrader/strategy.py", line 969, in sell
    **kwargs)
  File "/usr/local/lib/python3.7/site-packages/btoandav20/brokers/oandav20broker.py", line 315, in sell
    return self._transmit(order)
  File "/usr/local/lib/python3.7/site-packages/btoandav20/brokers/oandav20broker.py", line 272, in _transmit
    self.o.order_create(parent, stopside, takeside)
  File "/usr/local/lib/python3.7/site-packages/btoandav20/stores/oandav20store.py", line 385, in order_create
    '.%df' % order.data.contractdetails['displayPrecision']),
TypeError: unsupported format string passed to NoneType.__format__

At a glance, it looks like there might not be support for trailing stop by percent? https://github.com/ftomassetti/backtrader-oandav20/blob/master/btoandav20/stores/oandav20store.py#L384 If so, could it be added?

Thank you for the library! 👍