Strange results when using isQuantizedSequence() method

[mattebass]

Hi,
I'm actually using magenta.js in node and trying to parse some generated melodies.
In my code I need to know if the generated melody is quantised in order to pass to the model
When using:

mm.sequences.isQuantizedSequence(melody1)

let melody1 = {
    notes: [
      {pitch: 60, startTime: 0.0, endTime: 0.5},
      {pitch: 60, startTime: 0.5, endTime: 1.0},
      {pitch: 67, startTime: 1.0, endTime: 1.5},
      {pitch: 67, startTime: 1.5, endTime: 2.0},
      {pitch: 69, startTime: 2.0, endTime: 2.5},
      {pitch: 69, startTime: 2.5, endTime: 3.0},
      {pitch: 67, startTime: 3.0, endTime: 4.0},
      {pitch: 65, startTime: 4.0, endTime: 4.5},
      {pitch: 65, startTime: 4.5, endTime: 5.0},
      {pitch: 64, startTime: 5.0, endTime: 5.5},
      {pitch: 64, startTime: 5.5, endTime: 6.0},
      {pitch: 62, startTime: 6.0, endTime: 6.5},
      {pitch: 62, startTime: 6.5, endTime: 7.0},
      {pitch: 60, startTime: 7.0, endTime: 8.0},
    ],
    tempos: [{
      time: 0, 
      qpm: 120
    }],
    totalTime: 8
};


const melody2 = { 
    notes: [
        {pitch: 50, quantizedStartStep: 0, quantizedEndStep: 1},
        {pitch: 53, quantizedStartStep: 1, quantizedEndStep: 2},
        {pitch: 58, quantizedStartStep: 2, quantizedEndStep: 3},
        {pitch: 58, quantizedStartStep: 3, quantizedEndStep: 4},
        {pitch: 58, quantizedStartStep: 4, quantizedEndStep: 5},
        {pitch: 53, quantizedStartStep: 5, quantizedEndStep: 6},
        {pitch: 53, quantizedStartStep: 6, quantizedEndStep: 7},
        {pitch: 53, quantizedStartStep: 7, quantizedEndStep: 8},
        {pitch: 52, quantizedStartStep: 8, quantizedEndStep: 9},
        {pitch: 55, quantizedStartStep: 9, quantizedEndStep: 10},
        {pitch: 60, quantizedStartStep: 10, quantizedEndStep: 11},
        {pitch: 60, quantizedStartStep: 11, quantizedEndStep: 12},
        {pitch: 60, quantizedStartStep: 12, quantizedEndStep: 13},
        {pitch: 60, quantizedStartStep: 13, quantizedEndStep: 14},
        {pitch: 60, quantizedStartStep: 14, quantizedEndStep: 15},
        {pitch: 52, quantizedStartStep: 15, quantizedEndStep: 16},
        {pitch: 57, quantizedStartStep: 16, quantizedEndStep: 17},
        {pitch: 57, quantizedStartStep: 17, quantizedEndStep: 18},
        {pitch: 57, quantizedStartStep: 18, quantizedEndStep: 19},
        {pitch: 65, quantizedStartStep: 19, quantizedEndStep: 20},
        {pitch: 65, quantizedStartStep: 20, quantizedEndStep: 21},
        {pitch: 65, quantizedStartStep: 21, quantizedEndStep: 22},
        {pitch: 57, quantizedStartStep: 22, quantizedEndStep: 23},
        {pitch: 57, quantizedStartStep: 23, quantizedEndStep: 24},
        {pitch: 57, quantizedStartStep: 24, quantizedEndStep: 25},
        {pitch: 57, quantizedStartStep: 25, quantizedEndStep: 26},
        {pitch: 62, quantizedStartStep: 26, quantizedEndStep: 27},
        {pitch: 62, quantizedStartStep: 27, quantizedEndStep: 28},
        {pitch: 65, quantizedStartStep: 28, quantizedEndStep: 29},
        {pitch: 65, quantizedStartStep: 29, quantizedEndStep: 30},
        {pitch: 69, quantizedStartStep: 30, quantizedEndStep: 31},
        {pitch: 69, quantizedStartStep: 31, quantizedEndStep: 32}
        ],
    totalQuantizedSteps: 32,
    quantizationInfo: { stepsPerQuarter: 4 },
    tempos: [{time: 0, qpm: 120}]
};

the result is true if the melody is quantised as for melody2, but undefined if not as for melody1.
Is It a bug or I'm missing something?
Thanks