# Buggy code
def _worker(
    self, old_state: Optional[State], throttle_secs: Optional[float] = None
) -> State:
    """
    Trading routine that must be run at each loop
    :param old_state: the previous service state from the previous call
    :return: current service state
    """
    state = self.freqtrade.state
    if throttle_secs is None:
        throttle_secs = self._throttle_secs

    # Log state transition
    if state != old_state:
        self.freqtrade.notify_status(f"{state.name.lower()}")

        logger.info("Changing state to: %s", state.name)
        if state == State.RUNNING:
            self.freqtrade.startup()

    if state == State.STOPPED:
        # Ping systemd watchdog before sleeping in the stopped state
        if self._sd_notify:
            logger.debug("sd_notify: WATCHDOG=1\\nSTATUS=State: STOPPED.")
            self._sd_notify.notify("WATCHDOG=1\nSTATUS=State: STOPPED.")

        time.sleep(throttle_secs)

    elif state == State.RUNNING:
        # Ping systemd watchdog before throttling
        if self._sd_notify:
            logger.debug("sd_notify: WATCHDOG=1\\nSTATUS=State: RUNNING.")
            self._sd_notify.notify("WATCHDOG=1\nSTATUS=State: RUNNING.")

        self._throttle(func=self._process, min_secs=throttle_secs)

    return state


# 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 _worker(self, old_state: Optional[State]) -> State:
    """
    The main routine that runs each throttling iteration and handles the states.
    :param old_state: the previous service state from the previous call
    :return: current service state
    """
    state = self.freqtrade.state

    # Log state transition
    if state != old_state:
        self.freqtrade.notify_status(f"{state.name.lower()}")

        logger.info(f"Changing state to: {state.name}")
        if state == State.RUNNING:
            self.freqtrade.startup()

        # Reset heartbeat timestamp to log the heartbeat message at
        # first throttling iteration when the state changes
        self._heartbeat_msg = 0

    if state == State.STOPPED:
        # Ping systemd watchdog before sleeping in the stopped state
        if self._sd_notify:
            logger.debug("sd_notify: WATCHDOG=1\\nSTATUS=State: STOPPED.")
            self._sd_notify.notify("WATCHDOG=1\nSTATUS=State: STOPPED.")

        self._throttle(func=self._process_stopped, throttle_secs=self._throttle_secs)

    elif state == State.RUNNING:
        # Ping systemd watchdog before throttling
        if self._sd_notify:
            logger.debug("sd_notify: WATCHDOG=1\\nSTATUS=State: RUNNING.")
            self._sd_notify.notify("WATCHDOG=1\nSTATUS=State: RUNNING.")

        self._throttle(func=self._process_running, throttle_secs=self._throttle_secs)

    if self._heartbeat_interval:
        now = time.time()
        if (now - self._heartbeat_msg) > self._heartbeat_interval:
            logger.info(
                f"Bot heartbeat. PID={getpid()}, "
                f"version='{__version__}', state='{state.name}'"
            )
            self._heartbeat_msg = now

    return state