With the breakpoint at that first line, use the Step Over button (at the top of the right-hand-side panel) to step over the upTo line of code.
The link should be assigned something, but instead it is assigned
var link = upTo(button, ".linkse");
We know that
upTo is working properly now, so we can focus more clearly on the problem at hand without needing to be distracted by thoughts of the problem perhaps being inside of the upTo function itself.
We know (from the tests) that the problem is not in there, so why is the problem happening?
It's having trouble getting from that initiale element to the linkse element. It cannot find it by looking up, so what are we to do?
According to the HTML structure of your page, what should we be doing instead to get from the initiale section to the linkse section?