Assuming that the 'Target' tooltip always contains a certain string, like 'Target' as it does in your fiddle, you can amend the sparkline.js
file to behave how you want it to.
I have changed the following line in the sparkline.js
file, from:
if (!content) {
to check for the word 'Target', like so:
if (!content || (content.indexOf("Target") != -1)) {
Please note I have changed the External Resources
to point to a file on my server, which I will leave temporarily available.
If you check out this fiddle, it shows it working. I hope this helps!