Traceback (most recent call last):
  File "/usr/bin/gtimelog", line 1161, in on_last_month_report_activate
    self.mail(window.monthly_report)
  File "/usr/bin/gtimelog", line 1184, in mail
    write_draft(draft, self.settings.email, self.settings.name)
  File "/usr/bin/gtimelog", line 462, in monthly_report
    '(none)', format_duration_long(categories[None]))
KeyError: None