Error mapping US Zip codes with topojson

Error mapping US Zip codes with topojson

After loading a US zipcode topojson file I am getting an error in d3.js.
groupdata is undefined on this line:
function bind(group, groupData) {
var i, n = group.length, m = groupData.length, n0 = Math.min(n, m),
updateNodes = new Array(m), enterNodes = new Array(m), exitNodes =
new Array(n), node, nodeData;
with an error of:
Uncaught TypeError: Cannot read property 'length' of undefined
My code that is calling and creating the paths is:
d3.json("data/us-atlas/us-zipcodes.json", function(error, topology) {
svg.selectAll("path")
.data(topojson.feature(topology, topology.objects.zipcodes).features)
.enter()
.append("path")
.attr("d", path)
});
I generated the zipcode topojson file from this repo:
https://github.com/mbostock/us-atlas. When I inspect the topology object
on load I see 32893 arcs under topology.objects.zipcodes.
I have successfully loaded counties under with the chloropleth example
http://bl.ocks.org/mbostock/4060606 and am using a similar pattern as
that.
I'm using d3.js version 3.2.8 and topojson.js version 1.2.3.
Any ideas? Is it a bad zipcode file or am I calling it wrong?