Hide tooltip when no data on the point

c3.js

@@ -875,6 +875,8 @@
         function showTooltip(selectedData, mouse) {
             var tWidth, tHeight;
             var svgLeft, tooltipLeft, tooltipRight, tooltipTop, chartRight;
+            // don't show tooltip when no data
+            if (selectedData.filter(function (d) { return d.value; }).length === 0) { return; }
             // Construct tooltip
             tooltip.html(__tooltip_contents(selectedData))
                 .style("visibility", "hidden")