No fill / no stroke on text layer by scripting

Hi all,

I can't find a way to set a no fill color / no stroke color on a text layer. 

I can change the color, but the RGB color doesn't accept an alpha value. I tried with .setApplyFill(false) but it doesn't seem to work. Any ideas?

var mySourceText = layer.property("Source Text");
var textDocument = mySourceText.value;

// THIS CHANGE THE COLOR CORRECTLY
textDocument.fillColor = RGBcolor;    

mySourceText.setValue(textDocument);