Exception: A null Label has no root.

HI!
I have a simple question.
Has the TopoDS_Face generated from TopoDS_Shape a DF_Label or not ?:

Handle_XCAFDoc_ShapeTool aXCAFDoc_ShapeTool;
aXCAFDoc_ShapeTool = new XCAFDoc_ShapeTool();
aXCAFDoc_ShapeTool->Set(aRootTDF_Label);
TopoDS_Shape aTopoShape;
if(aXCAFDoc_ShapeTool->GetShape(aTopoShape,aOriginTopoShape))
{
TopTools_IndexedMapOfShape aFacesMap;
TopExp::MapShapes(aTopoShape,TopAbs_FACE,aFacesMap);
int aNumberOfShapes = aFacesMap.Extent();
TDF_Label aFaceShapeLabel;
for(int i=1;i {
TopoDS_Shape aFaceShape = aFacesMap(i);
try
{
aFaceShapeLabel = aXCAFDoc_ShapeTool->FindShape(aFaceShape,1); //!!!!Exception A null Label has no root.
....
}catch(...)
}
....