Temporary hack addressing issue in which a legend tries to redraw without available data.

legendredrawpatch.js

Y.CartesianChart.prototype._dataProviderChangeHandler = function(e) {
    var dataProvider = e.newVal,
        axes,
        i,
        axis;
    this._seriesIndex = -1;
    this._itemIndex = -1;
    this._drawing = true;
    if(this instanceof Y.CartesianChart)
    {
        this.set("axes", this.get("axes"));
        this.set("seriesCollection", this.get("seriesCollection"));
    }
    axes = this.get("axes");
    this._drawing = false;
    this._callLater = false;
    if(axes)
    {
        for(i in axes)
        {
            if(axes.hasOwnProperty(i))
            {
                axis = axes[i];
                if(axis instanceof Y.Axis)
                {
                    if(axis.get("position") !== "none")
                    {
                        this._addToAxesRenderQueue(axis);
                    }
                    axis.set("dataProvider", dataProvider);
                }
            }
        }
    }
};