serializeTree Method Returning Empty String

I have encountered a problem whilst serializing a tree into an XML representation for future use. I tried searching through the forums but found nothing on issues on the output of the tree in an XML representation.

The issue seems to be purely with the serializeTree method while the serializeToJSON appears to work correctly, although I do not want a JSON representation. The code does have the proper JavaScript file loaded to perform the method (dhtmlxtree_xw.js).

In the example below I use a simple JavaScript function; please ignore the lack of differentiation between html and scripts.

<a href="javascript:void(0);" onClick="exportXML();">Export XML</a>
function exportXML() {
   document.write(tree.serializeTree()); // writes an empty string
   // document.write(tree.serializeTreeToJSON()); // properly writes a JSON string representation
} // end exportXML
// some of the initialization of the tree
tree.loadCSV("tree_include/test_input.csv"); // anything that is loaded has the same problem

Thank you for any input.

Please check ready samples in Tree package:

serializeTree - dhtmlxSuite_v30_pro_111031/dhtmlxTree/samples/08_getting_tree_data/02_pro_user_data.html
loadCSVString - dhtmlxSuite_v30_pro_111031/dhtmlxTree/samples/11_json_support/02_pro_load_csv.html