code: function normalizeEncoding(enc) {
    var nenc = _normalizeEncoding(enc);
    if (typeof nenc !== 'string' && (Buffer.isEncoding === isEncoding || !isEncoding(enc))) throw new Error('Unknown encoding: ' + enc);
    return nenc || enc;
  }
docs: Do not cache `Buffer.isEncoding` when checking encoding names as some modules monkey-patch it to support additional encodings