esri.symbol.getShapeDescriptors() doesn't work with TextSymbol,why?

Discussion created by AttentiDev on Mar 6, 2012
I am trying to get the descriptors of my TextSymbol, but I received an object with undefined values, why?
At the API documentation it is mentioned that esri.symbol.getShapeDescriptors() should sent symbol parameter, and TextSymbol is inherited from Symbol class
Here is my code:

var arrowVectorSymbol = new esri.symbol.TextSymbol("\u00B6").setFont(new esri.symbol.Font("21px").setWeight(esri.symbol.Font.WEIGHT_BOLDER).setFamily("ESRI Cartogaphy"));
var descriptors = esri.symbol.getShapeDescriptors(arrowVectorSymbol);

The result I received:

descriptors = {defaultShape: undefined, fill: undefined, stroke: undefined};

Thanks for any help