TypeError: expected a character buffer object

[hut8]

  File "/usr/local/bin/format-sql", line 11, in <module>                                                                                                      
    sys.exit(main())                                                                                                                                          
  File "/usr/local/lib/python2.7/dist-packages/format_sql/main.py", line 83, in main                                                                          
    _write_back(filename, lines, args.dry_run)                                                                                                                
  File "/usr/local/lib/python2.7/dist-packages/format_sql/main.py", line 148, in _write_back                                                                  
    f.write(lines)                                                                                                                                            
TypeError: expected a character buffer object       

I've tried this with several files, including one ruby file with embedded SQL and then just with the SQL itself. Any insight into this? I'm just surprised that others aren't getting the same error.