TypeError: unsupported operand type(s) for -: 'datetime.datetime' and 'NoneType'

[Signum]

Version: 1.2

Thanks for maintaining the plugin. Works well on my Elegoo Neptune 3. However at "random" times the main log file is spammed with this message:

2022-11-26 21:09:56,650 - octoprint.util.comm - ERROR - Error while processing hook smartfilamentsensor for phase sent:
Traceback (most recent call last):
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint/util/comm.py", line 4670, in _process_command_phase
    tags=tags,
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint/util/__init__.py", line 1688, in wrapper
    return f(*args, **kwargs)
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint_smart_filament_sensor/__init__.py", line 401, in distance_detection
    self.calc_distance(float(extruder))
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint_smart_filament_sensor/__init__.py", line 272, in calc_distance
    if (datetime.now() - self.last_movement_time).total_seconds() > 10:
TypeError: unsupported operand type(s) for -: 'datetime.datetime' and 'NoneType'

It can easily be reproduced here using the VIRTUAL printer.

During a print yesterday that exception was raised 27,000 times.

[hviet17]

I have uploaded a fix #28, you can install via zip file or here https://github.com/hviet17/Octoprint-Smart-Filament-Sensor/archive/refs/heads/fix-operand.zip