Ordinal Scale Bug?

[Miles McCrocklin]

Reading the documentation, it implies that a specific domain is optional for d3.scale.ordinal(). 

However given this scale:

    var y = d3.scale.ordinal().rangeBands([0, h], .2);

y("anything") = undefined:

however when I do this:

function pullIdArray(data) {

    var s = {};

    data.forEach(function(d) { s[d._id] = true; });

    var ret = [];

    for (var k in s) {console.log(k); ret.push(k);}

    return ret;

}

var y = d3.scale.ordinal().domain(pullIdArray(data)).rangeBands([0, h], .2);

I get actual numerical values.

Can anyone tell me why this is?

[Mike Bostock]

A domain is required for rangeBands and rangePoints; otherwise, it
doesn't know how many bands or points to create.

Mike