code: function readFileSync(filename, cache, encoding=null) {
    if (cache.has(filename) && (cache.get(filename) !== true)) return cache.get(filename);
    const data = fs.readFileSync(filename, encoding);
    cache.set(filename, data);
    return data;
  }
docs: Read a file synchronously using file cache.
  
  @param {string} filename               The filename to load.
  @param {Map} cache                     The cache to use.
  @param {null|strin} [encoding=null]    The encoding to use.
  @returns {Buffer\*}                    The file contents as a buffer.