When two arrays are compared with isSet() and they are not the same then serialArray is called to display the actual and expected arrays. If serialArray is called with an array that has an undefined or null item in it then testrunner.js line 289:

var str = a[i].nodeName;

Throws a Type Error. Modifying this to:

var str = a[i] != undefined ? a[i].nodeName : undefined;

Appears to fix the problem.