class ActiveStorage::Filename

ActiveStorage::Filename.new(".gitignore").extension_with_delimiter # => ""
ActiveStorage::Filename.new("racecar").extension_with_delimiter # => ""
ActiveStorage::Filename.new("racecar.jpg").extension_with_delimiter # => ".jpg"

beginning) with the dot that precedes it. If the filename has no extension, an empty string is returned.
Returns the extension of the filename (i.e. the substring following the last dot, excluding a dot at the

def extension_with_delimiter
  File.extname @filename
end