Tooltip does not show when value is 0

Hi,

As per this example, (https://chrispahm.github.io/chartjs-plugin-dragData/bar.html), you can see that when value is 0, tooltip is visible. I'm having a problem that when value is 0, the tooltip is not popping up. Is there any options to correct for this. I'm using this for a drag and drop (using the above plugin), and without the tooltip I can't grab it at 0.

Thanks
Carl