# Buggy code
def _parse_args(self) -> argparse.Namespace:
    """
    Parses given arguments and returns an argparse Namespace instance.
    """
    parsed_arg = self.parser.parse_args(self.args)

    # Workaround issue in argparse with action='append' and default value
    # (see https://bugs.python.org/issue16399)
    # Allow no-config for certain commands (like downloading / plotting)
    if (
        "config" in parsed_arg
        and parsed_arg.config is None
        and (
            (Path.cwd() / constants.DEFAULT_CONFIG).is_file()
            or not ("command" in parsed_arg and parsed_arg.command in NO_CONF_REQURIED)
        )
    ):
        parsed_arg.config = [constants.DEFAULT_CONFIG]

    return parsed_arg


# 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 _parse_args(self) -> argparse.Namespace:
    """
    Parses given arguments and returns an argparse Namespace instance.
    """
    parsed_arg = self.parser.parse_args(self.args)

    # Workaround issue in argparse with action='append' and default value
    # (see https://bugs.python.org/issue16399)
    # Allow no-config for certain commands (like downloading / plotting)
    if "config" in parsed_arg and parsed_arg.config is None:
        conf_required = (
            "command" in parsed_arg and parsed_arg.command in NO_CONF_REQURIED
        )

        if "user_data_dir" in parsed_arg and parsed_arg.user_data_dir is not None:
            user_dir = parsed_arg.user_data_dir
        else:
            # Default case
            user_dir = "user_data"
            # Try loading from "user_data/config.json"
        cfgfile = Path(user_dir) / DEFAULT_CONFIG
        if cfgfile.is_file():
            parsed_arg.config = [str(cfgfile)]
        else:
            # Else use "config.json".
            cfgfile = Path.cwd() / DEFAULT_CONFIG
            if cfgfile.is_file() or not conf_required:
                parsed_arg.config = [DEFAULT_CONFIG]

    return parsed_arg