# Buggy code
def _rpc_forcesell(self, trade_id) -> Dict[str, str]:
    """
    Handler for forcesell <id>.
    Sells the given trade at current price
    """

    def _exec_forcesell(trade: Trade) -> None:
        # Check if there is there is an open order
        if trade.open_order_id:
            order = self._freqtrade.exchange.get_order(trade.open_order_id, trade.pair)

            # Cancel open LIMIT_BUY orders and close trade
            if (
                order
                and order["status"] == "open"
                and order["type"] == "limit"
                and order["side"] == "buy"
            ):
                self._freqtrade.exchange.cancel_order(trade.open_order_id, trade.pair)
                trade.close(order.get("price") or trade.open_rate)
                # Do the best effort, if we don't know 'filled' amount, don't try selling
                if order["filled"] is None:
                    return
                trade.amount = order["filled"]

            # Ignore trades with an attached LIMIT_SELL order
            if (
                order
                and order["status"] == "open"
                and order["type"] == "limit"
                and order["side"] == "sell"
            ):
                return

        # Get current rate and execute sell
        current_rate = self._freqtrade.get_sell_rate(trade.pair, False)
        self._freqtrade.execute_sell(trade, current_rate, SellType.FORCE_SELL)

    # ---- EOF def _exec_forcesell ----

    if self._freqtrade.state != State.RUNNING:
        raise RPCException("trader is not running")

    with self._freqtrade._sell_lock:
        if trade_id == "all":
            # Execute sell for all open orders
            for trade in Trade.get_open_trades():
                _exec_forcesell(trade)
            Trade.session.flush()
            self._freqtrade.wallets.update()
            return {"result": "Created sell orders for all open trades."}

        # Query for trade
        trade = Trade.get_trades(
            trade_filter=[
                Trade.id == trade_id,
                Trade.is_open.is_(True),
            ]
        ).first()
        if not trade:
            logger.warning("forcesell: Invalid argument received")
            raise RPCException("invalid argument")

        _exec_forcesell(trade)
        Trade.session.flush()
        self._freqtrade.wallets.update()
        return {"result": f"Created sell order for trade {trade_id}."}


# Traceback (Exception)
2020-02-20 22:47:28,025 - freqtrade - ERROR - Fatal exception!
Traceback (most recent call last):
File "/opt/tradebot/freqtrade/.env/lib/python3.7/site-packages/talib/__init__.py", line 20, in wrapper
for arg in chain(args, kwargs.values())
StopIteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/freqtrade/freqtrade/main.py", line 36, in main
return_code = args['func'](args)
File "/freqtrade/freqtrade/commands/optimize_commands.py", line 76, in start_hyperopt
hyperopt.start()
File "/freqtrade/freqtrade/optimize/hyperopt.py", line 488, in start
preprocessed = self.backtesting.strategy.tickerdata_to_dataframe(data)
File "/freqtrade/freqtrade/strategy/interface.py", line 448, in tickerdata_to_dataframe
for pair, pair_data in tickerdata.items()}
File "/freqtrade/freqtrade/strategy/interface.py", line 448, in <dictcomp>
for pair, pair_data in tickerdata.items()}
File "/freqtrade/freqtrade/strategy/interface.py", line 464, in advise_indicators
return self.populate_indicators(dataframe, metadata)
File "/freqtrade/user_data/strategies/MyDev.py", line 205, in populate_indicators
dataframe['mfi'] = ta.MFI(dataframe)
File "talib/_abstract.pxi", line 352, in talib._ta_lib.Function.__call__
File "talib/_abstract.pxi", line 383, in talib._ta_lib.Function.__call_function
File "/opt/tradebot/freqtrade/.env/lib/python3.7/site-packages/talib/__init__.py", line 24, in wrapper
return func(*args, **kwargs)
File "talib/_func.pxi", line 8454, in talib._ta_lib.MFI
Exception: volume is not double

# Fixed code
def _rpc_forcesell(self, trade_id: str) -> Dict[str, str]:
    """
    Handler for forcesell <id>.
    Sells the given trade at current price
    """

    def _exec_forcesell(trade: Trade) -> None:
        # Check if there is there is an open order
        if trade.open_order_id:
            order = self._freqtrade.exchange.get_order(trade.open_order_id, trade.pair)

            # Cancel open LIMIT_BUY orders and close trade
            if (
                order
                and order["status"] == "open"
                and order["type"] == "limit"
                and order["side"] == "buy"
            ):
                self._freqtrade.exchange.cancel_order(trade.open_order_id, trade.pair)
                trade.close(order.get("price") or trade.open_rate)
                # Do the best effort, if we don't know 'filled' amount, don't try selling
                if order["filled"] is None:
                    return
                trade.amount = order["filled"]

            # Ignore trades with an attached LIMIT_SELL order
            if (
                order
                and order["status"] == "open"
                and order["type"] == "limit"
                and order["side"] == "sell"
            ):
                return

        # Get current rate and execute sell
        current_rate = self._freqtrade.get_sell_rate(trade.pair, False)
        self._freqtrade.execute_sell(trade, current_rate, SellType.FORCE_SELL)

    # ---- EOF def _exec_forcesell ----

    if self._freqtrade.state != State.RUNNING:
        raise RPCException("trader is not running")

    with self._freqtrade._sell_lock:
        if trade_id == "all":
            # Execute sell for all open orders
            for trade in Trade.get_open_trades():
                _exec_forcesell(trade)
            Trade.session.flush()
            self._freqtrade.wallets.update()
            return {"result": "Created sell orders for all open trades."}

        # Query for trade
        trade = Trade.get_trades(
            trade_filter=[
                Trade.id == trade_id,
                Trade.is_open.is_(True),
            ]
        ).first()
        if not trade:
            logger.warning("forcesell: Invalid argument received")
            raise RPCException("invalid argument")

        _exec_forcesell(trade)
        Trade.session.flush()
        self._freqtrade.wallets.update()
        return {"result": f"Created sell order for trade {trade_id}."}