如何在flutter中找到地图最大值的键？

Map themap={"anger": 0.0, "contempt": 0.02, "disgust": 0.0, "fear": 2.0, "happiness": 0.0, "neutral": 0.978, "sadness": 0.002, "surprise": 0.0};

    var thevalue=0.0;
    var thekey;

    themap.forEach((k,v){
      if(v>thevalue) {
        thevalue = v;
        thekey = k;
      }
    });

    print (thekey);