# Buggy code
def _override_attribute_helper(strategy, config, attribute: str, default):
    """
    Override attributes in the strategy.
    Prevalence:
    - Configuration
    - Strategy
    - default (if not None)
    """
    if attribute in config:
        setattr(strategy, attribute, config[attribute])
        logger.info(
            "Override strategy '%s' with value in config file: %s.",
            attribute,
            config[attribute],
        )
    elif hasattr(strategy, attribute):
        val = getattr(strategy, attribute)
        # None's cannot exist in the config, so do not copy them
        if val is not None:
            config[attribute] = val
    # Explicitly check for None here as other "falsy" values are possible
    elif default is not None:
        setattr(strategy, attribute, default)
        config[attribute] = default


# 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 _override_attribute_helper(
    strategy, config: Dict[str, Any], attribute: str, default: Any
):
    """
    Override attributes in the strategy.
    Prevalence:
    - Configuration
    - Strategy
    - default (if not None)
    """
    if attribute in config:
        setattr(strategy, attribute, config[attribute])
        logger.info(
            "Override strategy '%s' with value in config file: %s.",
            attribute,
            config[attribute],
        )
    elif hasattr(strategy, attribute):
        val = getattr(strategy, attribute)
        # None's cannot exist in the config, so do not copy them
        if val is not None:
            config[attribute] = val
    # Explicitly check for None here as other "falsy" values are possible
    elif default is not None:
        setattr(strategy, attribute, default)
        config[attribute] = default