Duplicate strings to avoid freezing empty strings casted from nil
Duplicate strings to avoid freezing empty strings casted from nil

Closes: https://github.com/norman/babosa/issues/51

Objects can be nil, which when cast to Strings yield frozen strings [0]
which cannot be mutated using methods like `downcase!`.

[0] https://bugs.ruby-lang.org/issues/16150?next_issue_id=16184

Signed-off-by: Balasankar "Balu" C <0bac1367e81975601fd06ab8b2ef22d05b331732@autistici.org>

norman/babosa