use strings as immutable default arguments

[benjdevries]

Fixes #161

Avoid using mutable objects as default arguments as functions. Even though this particular usage was safe, it opens up the projects to issues down the road if the default argument is mutated within the function. For this usage, we don't need an actual list object, just a sequence of strings, so we can use a string itself.

[benjdevries]

I'm a first time contributor. Please let me know if I should update the PR title or description or if there is any documentation that needs to be updated as well. Thanks!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.19%. Comparing base (e927322) to head (b3e3e5a).

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Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #162   +/-   ##
========================================
  Coverage    97.19%   97.19%           
========================================
  Files            8        8           
  Lines          214      214           
  Branches        46       46           
========================================
  Hits           208      208           
  Misses           3        3           
  Partials         3        3           

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[kislyuk]

Thanks for contributing! I will check the docs/linting and make a new release soon.