Node.js+lame - TypeError: string is not a function

I want to read an audi file with Node.js, decode it to PCM and encode it as a MP3. I'm using node-lame to do the en-/decoding, but unfortunately I get the following error:

/Users/Jon/streaming test/node_modules/lame/lib/encoder.js:191
  write(output);
  ^
TypeError: string is not a function
at cb (/Users/Jon/streaming test/node_modules/lame/lib/encoder.js:191:7)

My code for the encoding and decoding:

var filename = './beautifullie.mp3';
var decoder = lame.Decoder();
var encoder = lame.Encoder({channels: 2, bitDepth: 16, sampleRate: 44100});

fs.createReadStream(filename).pipe(decoder);

decoder.on('format', function(format) {
  console.log('Decoding .. '+JSON.stringify(format));
  decoder.pipe(encoder);
});

encoder.on("data", function(data) {
  console.log('Sending..');
  //sendData(data);
});

You can find the file that throws the error here: https://github.com/TooTallNate/node-lame/blob/master/lib/encoder.js