NameError: name 'backup_tool' is not defined

[nsteinbach]

When trying to import a SMS backup (or just run the script with or without any options), I always get the following error message:

$ python sms_import.py
Traceback (most recent call last):
  File "sms_import.py", line 3, in <module>
    from sail_sms import SMSParser, SMSImporter, SMSBackup
  File "/home/nemo/Downloads/sail_sms.py", line 282, in <module>
    backup_tool.create_backup()
NameError: name 'backup_tool' is not defined

Running on SailfishOS 3.0.0.8 on Sony XPeria X ("Sailfish X").
Same error message, no matter if I use python2 or python3 to run the script.
What requirement is my device missing for the script to work?