fix(chart-heatfield): Chart Heatfield is now hidden when start and en…

…d are undefined

- Button/heatfield is now hidden if both start and end are undefined
- Added test to check for start and end being both undefined

libs/barista-components/chart/src/heatfield/chart-heatfield.html

@@ -1,6 +1,7 @@
 <button
   class="dt-chart-heatfield-marker"
   [class.dt-chart-heatfield-active]="active"
+  [style.visibility]="_isValidStartEndRange ? 'visible' : 'hidden'"
   #marker="cdkOverlayOrigin"
   cdk-overlay-origin
   (click)="_toggleActive()"

libs/barista-components/chart/src/heatfield/chart-heatfield.spec.ts

@@ -133,6 +133,14 @@ describe('DtChartHeatfield', () => {
         chart._afterRender.next();
         validatePosition(fixture, 100, 500);
       });
+
+      it('should not render heatfield when start and end are undefined ', () => {
+        instance.start = undefined;
+        instance.end = undefined;
+        fixture.detectChanges();
+        chart._afterRender.next();
+        expect(marker.style.visibility).toEqual('hidden');
+      });
     });
 
     describe('Activation', () => {