fix non-existing metrics being highlighted on hover

src/index.ts

@@ -221,7 +221,7 @@ export class LinePod extends ChartwerkPod<LineTimeSerie, LineOptions> {
       default:
         throw new Error(`Unknown type of crosshair orientaion: ${this.options.crosshair.orientation}`);
     }
-    
+
     // TODO: d3.bisect is not the best way. Use binary search
     const bisectIndex = d3.bisector((d: [number, number]) => d[columnIdx]).left;
     let closestIdx = bisectIndex(datapoints, value);
@@ -290,14 +290,18 @@ export class LinePod extends ChartwerkPod<LineTimeSerie, LineOptions> {
     let points = []; // datapoints in each metric that is closest to xValue/yValue position
     this.series.visibleSeries.forEach((serie: LineTimeSerie) => {
       const closestDatapoint = this.getClosestDatapoint(serie, xValue, yValue);
-      if(closestDatapoint === undefined) {
+      if(_.isNil(closestDatapoint)) {
         this.hideCrosshairCircle(serie.idx);
         return;
       }
 
       const xPosition = this.state.xScale(closestDatapoint[0]);
       const yPosition = this.state.yScale(closestDatapoint[1]);
-      this.moveCrosshairCircle(xPosition, yPosition, serie.idx);
+      if(!_.isNil(closestDatapoint[0])) {
+        this.moveCrosshairCircle(xPosition, yPosition, serie.idx);
+      } else {
+        this.hideCrosshairCircle(serie.idx);
+      }
 
       points.push({
         value: closestDatapoint,
@@ -357,7 +361,7 @@ export class LinePod extends ChartwerkPod<LineTimeSerie, LineOptions> {
     this.renderYAxis();
     this.renderGrid();
     this.onMouseOver();
-    
+
     let xAxisMiddleValue: number = this.state.xScale.invert(this.width / 2);
     let yAxisMiddleValue: number = this.state.yScale.invert(this.height / 2);
     const centers = {