fix non-existing metrics being highlighted on hover

src/index.ts

@@ -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]);
+      if(!_.isNil(closestDatapoint[0])) {
         this.moveCrosshairCircle(xPosition, yPosition, serie.idx);
+      } else {
+        this.hideCrosshairCircle(serie.idx);
+      }
 
       points.push({
         value: closestDatapoint,