25 + 5 Clock 2 tests fail and I don't get how to solve them

Hey guys I need to pass just 2 tests in order to get a pass for my 25 + 5 Clock project.
There seems to be an Issue when my Countdown, doesn’t matter if its a Session or a Break, gets to zero(00:00). The test suit says the following:" When a session countdown reaches zero (NOTE: timer MUST reach 00:00), and a new countdown begins, the element with the id of “timer-label” should display a string indicating a break has begun." And I get an error message of : “null is not an object (evaluating ‘s.exec(e)[1]’)”.
I guess it has something to do with how I store the setInterval()- function within my state. The code that handles the switch between Session and break is within my setTime()-method. Hope somebody can help me out.

Heres the link to my project: