...
fileTypes[".wav"] = true
fileTypes[".flac"] = true
...
            -- local extension = string.lower(string.sub(file, -4))
            -- Regex Explanation: https://gitspartv.github.io/lua-patterns/?pattern=%25.%5B%25a%25d%5D%2B%24
            local extension = string.lower(string.match(file, '%.[%a%d]+$') or '')
...