How to specify default File name in AX2012 R3

Hi all,

Please let me know how to give a default file name in AX.

This is the code for running dialog:

FilenameOpen fileNameOpen;
DialogField dialogFileName;
Dialog dialog;
Filename fileName;
;

dialog = new Dialog("Move Files");
dialogFileName = dialog.addField(extendedTypeStr(FileNameOpen));
dialogFilename.value("File 1");
dialog.run();

When I'm running this script through job 

output :

When clicking on marked image for selecting location the default file name became empty as below

I would like to keep the default File name "File 1".

Kindly let me know how to assign default file name?