ZingChart X轴标签显示为数字而不是字符串

Question

我正在使用ZingChart库来绘制API调用的结果。当我为图表数据对象的“值”字段传入一个普通数组时，一切正常。但是，当我传入由Object.keys(titleSet)（其中titleSet是普通Javascript对象）的数组时，图表显示如下：

Example Chart

如您所见，x轴现在标有数字而不是字符串数组。但是当我打印出Object.keys(titleSet)与传入正常数组的结果时，它们在控制台中看起来都是相同的。谁能帮我弄清楚我做错了什么？

//List of movies inputted by the user
var movieList = [];
var movieSet = {};

var IMDBData = {
  "values": [], 
  "text": "IMDB",
};
var metascoreData = {
  "values": [], 
  "text": "Metascore"
};
var RTMData = {
  "values": [], 
  "text": "Rotten Tomatoes Meter"
};
var RTUData = {
  "values": [],
   "text": "Rotten Tomatoes User"
};

var chartData = { 
  "type":"bar",
  "legend":{
    "adjust-layout": true
  },
  "plotarea": {
    "adjust-layout":true
  },
  "plot":{ 
    "stacked": true,
    "border-radius": "1px",
    "tooltip": {
      "text": "Rated %v by %plot-text"
    },
    "animation":{
      "effect":"11",
      "method":"3",
      "sequence":"ANIMATION_BY_PLOT_AND_NODE",
      "speed":10
    } 
  },
  "scale-x": {
    "label":{ /* Scale Title */
      "text":"Movie Title",
    },
    "values": Object.keys(movieSet) /* Needs to be list of movie titles */
  },
  "scale-y": {
    "label":{ /* Scale Title */
      "text":"Total Score",
    }
  },
  "series":[metascoreData, IMDBData, RTUData, RTMData]
};


var callback = function(data)
{
  var resp = JSON.parse(data);

  movieSet[resp.Title] = true;

  //Render
  zingchart.render({ 
    id:'chartDiv',
    data:chartData,
  });
};