Exception when log format is unspecified

[MJafarMashhadi]

Exception while notifying an observer of flight_param
Traceback (most recent call last):
  File "/home/ict520c/Documents/pprz_tester/pprz_tester/aircraft.py", line 84, in _notify_all
    cb(property_name=name, old_value=old_value, new_value=new_value)
  File "/home/ict520c/Documents/pprz_tester/pprz_tester/observer.py", line 6, in __call__
    self.notify(property_name, old_value, new_value)
  File "/home/ict520c/Documents/pprz_tester/pprz_tester/flight_recorder.py", line 58, in notify
    self.save_history()
  File "/home/ict520c/Documents/pprz_tester/pprz_tester/flight_recorder.py", line 65, in save_history
    raise ValueError(f"Unrecognised log format {log_format}")
ValueError: Unrecognised log format c