externalRadiusPadding (externalRadiusPadding) {
        if (!arguments.length) {
            return this._externalRadiusPadding;
        }
        this._externalRadiusPadding = externalRadiusPadding;
        return this;
    }
Get or set the external radius padding of the pie chart. This will force the radius of the
pie chart to become smaller or larger depending on the value.
@param {Number} [externalRadiusPadding=0]
@returns {Number|PieChart}