Chart.js，未捕获的TypeError：无法设置未定义的属性“ 0”

Question

我正在使用Chart.js制作一个折线图，该折线图最初所有的数据点都为null。我尝试一次更新一个点，具体取决于renovation_val。这是导致错误的行：

line_chart.data.datasets.data[0] = 2500*1.2*mults;

该错误表明data数组未定义，但我不确定如何解决。

JavaScript代码：

line_chart = new Chart(profit_chart, {
      type: 'line',
      data:{
        labels:['$2,500','$5,000','$7,500','$10,000','$12,500','$15,000','$17,500','$20,000','$22,500','$25,000','$27,500','$30,000','$32,500','$35,000','$37,500','$40,000','$42,500','$45,000','$47,500','$50,000'],
        datasets:[{
          label:'Profit ($)',
          data: [null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null,null],
          backgroundColor: 'rgba(255, 255, 255, 0.2)',
          borderColor: '#333',
        }],
      },
      options:{
		tooltips:{
			enabled:false
		},
        title:{
          fontFamily: 'Nunito',
        },
        legend: {
          	display: false,
            labels: {
                fontColor: "#000",
                fontSize: 18
            },
        },
        scales:{
          xAxes: [{
            gridLines: {
                    display: false,
                    lineWidth: 2,
                },
            ticks: {
              fontFamily: 'Nunito',
                  fontColor: "#000", // this here
				  autoSkip:false,
                },
            scaleLabel: {
              display: true,
              labelString: "Budget",
              fontFamily: 'Nunito',
              fontColor: "#000", // this here
            },
          }],
          yAxes: [{
            gridLines: {
                    display: false,
                    lineWidth: 2,
                },
            ticks: {
              fontFamily: 'Nunito',
              	beginAtZero: true,
                  fontColor: "#000", // this here
                },
            scaleLabel: {
              display: true,
              labelString: "Profit",
              fontFamily: 'Nunito',
              fontColor: "#000", // this here
            },
          }],
        },
      }
    });
	switch(renovation_val) {
		case 2500:
			line_chart.data.datasets.data[0] = 2500*1.2*mults;
			line_chart.update();
			break;
	};