# Buggy code
def get_buy_rate(self, pair: str, tick: Dict = None) -> float:
    """
    Calculates bid target between current ask price and last price
    :return: float: Price
    """
    config_bid_strategy = self.config.get("bid_strategy", {})
    if "use_order_book" in config_bid_strategy and config_bid_strategy.get(
        "use_order_book", False
    ):
        logger.info("Getting price from order book")
        order_book_top = config_bid_strategy.get("order_book_top", 1)
        order_book = self.exchange.get_order_book(pair, order_book_top)
        logger.debug("order_book %s", order_book)
        # top 1 = index 0
        order_book_rate = order_book["bids"][order_book_top - 1][0]
        logger.info(
            "...top %s order book buy rate %0.8f", order_book_top, order_book_rate
        )
        used_rate = order_book_rate
    else:
        if not tick:
            logger.info("Using Last Ask / Last Price")
            ticker = self.exchange.fetch_ticker(pair)
        else:
            ticker = tick
        if ticker["ask"] < ticker["last"]:
            ticker_rate = ticker["ask"]
        else:
            balance = self.config["bid_strategy"]["ask_last_balance"]
            ticker_rate = ticker["ask"] + balance * (ticker["last"] - ticker["ask"])
        used_rate = ticker_rate

    return used_rate


# 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 get_buy_rate(self, pair: str, refresh: bool) -> float:
    """
    Calculates bid target between current ask price and last price
    :param pair: Pair to get rate for
    :param refresh: allow cached data
    :return: float: Price
    """
    if not refresh:
        rate = self._buy_rate_cache.get(pair)
        # Check if cache has been invalidated
        if rate:
            logger.info(f"Using cached buy rate for {pair}.")
            return rate

    config_bid_strategy = self.config.get("bid_strategy", {})
    if "use_order_book" in config_bid_strategy and config_bid_strategy.get(
        "use_order_book", False
    ):
        logger.info("Getting price from order book")
        order_book_top = config_bid_strategy.get("order_book_top", 1)
        order_book = self.exchange.get_order_book(pair, order_book_top)
        logger.debug("order_book %s", order_book)
        # top 1 = index 0
        order_book_rate = order_book["bids"][order_book_top - 1][0]
        logger.info(
            "...top %s order book buy rate %0.8f", order_book_top, order_book_rate
        )
        used_rate = order_book_rate
    else:
        logger.info("Using Last Ask / Last Price")
        ticker = self.exchange.fetch_ticker(pair)
        if ticker["ask"] < ticker["last"]:
            ticker_rate = ticker["ask"]
        else:
            balance = self.config["bid_strategy"]["ask_last_balance"]
            ticker_rate = ticker["ask"] + balance * (ticker["last"] - ticker["ask"])
        used_rate = ticker_rate

    self._buy_rate_cache[pair] = used_rate

    return used_rate