# Buggy code
def execute_sell(self, trade: Trade, limit: float, sell_reason: SellType) -> None:
    """
    Executes a limit sell for the given trade and limit
    :param trade: Trade instance
    :param limit: limit rate for the sell order
    :param sellreason: Reason the sell was triggered
    :return: None
    """
    sell_type = "sell"
    if sell_reason in (SellType.STOP_LOSS, SellType.TRAILING_STOP_LOSS):
        sell_type = "stoploss"

    # if stoploss is on exchange and we are on dry_run mode,
    # we consider the sell price stop price
    if (
        self.config["dry_run"]
        and sell_type == "stoploss"
        and self.strategy.order_types["stoploss_on_exchange"]
    ):
        limit = trade.stop_loss

    # First cancelling stoploss on exchange ...
    if (
        self.strategy.order_types.get("stoploss_on_exchange")
        and trade.stoploss_order_id
    ):
        try:
            self.exchange.cancel_order(trade.stoploss_order_id, trade.pair)
        except InvalidOrderException:
            logger.exception(
                f"Could not cancel stoploss order {trade.stoploss_order_id}"
            )

    order_type = self.strategy.order_types[sell_type]
    if sell_reason == SellType.EMERGENCY_SELL:
        # Emergencysells (default to market!)
        order_type = self.strategy.order_types.get("emergencysell", "market")

    amount = self._safe_sell_amount(trade.pair, trade.amount)

    # Execute sell and update trade record
    order = self.exchange.sell(
        pair=str(trade.pair),
        ordertype=order_type,
        amount=amount,
        rate=limit,
        time_in_force=self.strategy.order_time_in_force["sell"],
    )

    trade.open_order_id = order["id"]
    trade.close_rate_requested = limit
    trade.sell_reason = sell_reason.value
    # In case of market sell orders the order can be closed immediately
    if order.get("status", "unknown") == "closed":
        trade.update(order)
    Trade.session.flush()

    # Lock pair for one candle to prevent immediate rebuys
    self.strategy.lock_pair(
        trade.pair, timeframe_to_next_date(self.config["ticker_interval"])
    )

    self._notify_sell(trade, order_type)


# 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 execute_sell(self, trade: Trade, limit: float, sell_reason: SellType) -> bool:
    """
    Executes a limit sell for the given trade and limit
    :param trade: Trade instance
    :param limit: limit rate for the sell order
    :param sellreason: Reason the sell was triggered
    :return: True if it succeeds (supported) False (not supported)
    """
    sell_type = "sell"
    if sell_reason in (SellType.STOP_LOSS, SellType.TRAILING_STOP_LOSS):
        sell_type = "stoploss"

    # if stoploss is on exchange and we are on dry_run mode,
    # we consider the sell price stop price
    if (
        self.config["dry_run"]
        and sell_type == "stoploss"
        and self.strategy.order_types["stoploss_on_exchange"]
    ):
        limit = trade.stop_loss

    # First cancelling stoploss on exchange ...
    if (
        self.strategy.order_types.get("stoploss_on_exchange")
        and trade.stoploss_order_id
    ):
        try:
            self.exchange.cancel_order(trade.stoploss_order_id, trade.pair)
        except InvalidOrderException:
            logger.exception(
                f"Could not cancel stoploss order {trade.stoploss_order_id}"
            )

    order_type = self.strategy.order_types[sell_type]
    if sell_reason == SellType.EMERGENCY_SELL:
        # Emergency sells (default to market!)
        order_type = self.strategy.order_types.get("emergencysell", "market")

    amount = self._safe_sell_amount(trade.pair, trade.amount)

    # Execute sell and update trade record
    order = self.exchange.sell(
        pair=str(trade.pair),
        ordertype=order_type,
        amount=amount,
        rate=limit,
        time_in_force=self.strategy.order_time_in_force["sell"],
    )

    trade.open_order_id = order["id"]
    trade.close_rate_requested = limit
    trade.sell_reason = sell_reason.value
    # In case of market sell orders the order can be closed immediately
    if order.get("status", "unknown") == "closed":
        trade.update(order)
    Trade.session.flush()

    # Lock pair for one candle to prevent immediate rebuys
    self.strategy.lock_pair(
        trade.pair, timeframe_to_next_date(self.config["ticker_interval"])
    )

    self._notify_sell(trade, order_type)

    return True