Error: Assertion failed: y should be a finite number
at window.assertions.assertFunction (http://phettest.colorado.edu/assert/js/assert.js:23:13)
at Node.setY (http://phettest.colorado.edu/scenery/js/nodes/Node.js?bust=1479837330859:1875:17)
at Node.set y [as y] (http://phettest.colorado.edu/scenery/js/nodes/Node.js?bust=1479837330859:1880:27)
at updateTheString (http://phettest.colorado.edu/wave-on-a-string/js/wave-on-a-string/view/action/TheStringNode.js?bust=1479837330859:61:26)
at Array. (http://phettest.colorado.edu/wave-on-a-string/js/wave-on-a-string/view/action/TheStringNode.js?bust=1479837330859:75:9)
at Emitter.emit (http://phettest.colorado.edu/axon/js/Emitter.js?bust=1479837330859:106:49)
at WOASView.step (http://phettest.colorado.edu/wave-on-a-string/js/wave-on-a-string/view/WOASView.js?bust=1479837330859:240:18)
at Sim.stepSimulation (http://phettest.colorado.edu/joist/js/Sim.js?bust=1479837330859:691:25)
at Sim.runAnimationLoop (http://phettest.colorado.edu/joist/js/Sim.js?bust=1479837330859:627:12)