`NoneType` and string concatenation when exporting with deleted expenses

[kantoniak]

I get TypeError when running the script with Include deleted expenses? option enabled:

Traceback (most recent call last):
  File "/splitwise_export/splitwise_export.py", line 173, in <module>
    main()
  File "<redacted>/splitwise_export/splitwise_export.py", line 170, in main
    expenses_to_csv(expenses)
  File "<redacted>/splitwise_export/splitwise_export.py", line 156, in expenses_to_csv
    df['Deleted'] = df.apply(lambda row: get_user_name(row['Deleted']), axis=1)
  File "<redacted>/.local/share/virtualenvs/splitwise_export-vGNwKnlj/lib/python3.10/site-packages/pandas/core/frame.py", line 10034, in apply
    return op.apply().__finalize__(self, method="apply")
  File "<redacted>/.local/share/virtualenvs/splitwise_export-vGNwKnlj/lib/python3.10/site-packages/pandas/core/apply.py", line 837, in apply
    return self.apply_standard()
  File "<redacted>/.local/share/virtualenvs/splitwise_export-vGNwKnlj/lib/python3.10/site-packages/pandas/core/apply.py", line 965, in apply_standard
    results, res_index = self.apply_series_generator()
  File "<redacted>/.local/share/virtualenvs/splitwise_export-vGNwKnlj/lib/python3.10/site-packages/pandas/core/apply.py", line 981, in apply_series_generator    results[i] = self.func(v, *self.args, **self.kwargs)
  File "<redacted>/splitwise_export/splitwise_export.py", line 156, in <lambda>
    df['Deleted'] = df.apply(lambda row: get_user_name(row['Deleted']), axis=1)
  File "<redacted>/splitwise_export/splitwise_export.py", line 102, in get_user_name
    return user.getFirstName() + " " + user.getLastName()
TypeError: can only concatenate str (not "NoneType") to str

Exporter works fine otherwise. I added print(user) as a quick check, and in all but one invocation user == None. I'm happy to provide more details should you need any.