0x800a138f - JavaScript runtime error - IE11 compatibility with d3

I'm building a d3 treemap based off of the zoomable treemap found at http://bl.ocks.org/davetaz/9954190. I have everything working fine in chrome/firefox/etc, but company standard is IE11 so it needs to be compatible. Each time I run it in IE, I get the following error: "Unhandled exception at line 70, column 5... 0x800a138f - JavaScript runtime error: Unable to get property 'children' of undefined or null reference". I've tried a couple of other solutions that have been posted for other issues but none of them seem to work. The error is in the original code itself, in the treemap.js file, and launching the original template results in the same error. It's thrown with the following:

function accumulate(d) {
    return (d._children = d.children)
    ? d.value = d.children.reduce(function (p, v) { return p + accumulate(v); }, 0)
    : d.value;
}

Any help would be appreciated. Thanks!