message: fix(canvas/painter): ctx was mistakenly assigned with a null value. fix apache/echarts#14112.
diff: @@ -926,24 +926,24 @@ export default class CanvasPainter implements PainterBase {
  }
  const imageLayer = new Layer('image', this, opts.pixelRatio || this.dpr);
  - const ctx = imageLayer.ctx;
  imageLayer.initContext();
  imageLayer.clear(false, opts.backgroundColor || this._backgroundColor);
  + const ctx = imageLayer.ctx;
  +
  if (opts.pixelRatio <= this.dpr) {
  this.refresh();
  const width = imageLayer.dom.width;
  const height = imageLayer.dom.height;
  - const ctx = imageLayer.ctx;
  this.eachLayer(function (layer) {
  if (layer.__builtin__) {
  ctx.drawImage(layer.dom, 0, 0, width, height);
  }
  else if (layer.renderToCanvas) {
  - imageLayer.ctx.save();
  - layer.renderToCanvas(imageLayer.ctx);
  - imageLayer.ctx.restore();
  + ctx.save();
  + layer.renderToCanvas(ctx);
  + ctx.restore();
  }
  });
  }
  