🚀 go-pugleaf

I have a simple JS to create a new 6 column document, however I cannot get 'TextColumnCount' to work. Can anyone see where I'm going wrong here?
Thanks

var myDocument = app.documents.add();
with(myDocument.documentPreferences){
	pageHeight = "297mm";
	pageWidth = "210mm";
	pageOrientation = PageOrientation.portrait;
	facingPages = false;
}
with(myDocument.textDefaults){
	kerningMethod = "Metrics";
	appliedFont = "Arial";
}
with(myDocument.pages.item(0)){
	with(marginPreferences){
		columnCount = 6;
		columnGutter = "4.233mm";
		bottom = "12.7mm";
		left = "12.7mm";
		right = "12.7mm";
		top = "12.7mm";
	}
	with(textFrames.add()){
		geometricBounds = ["12.7mm", "12.7mm", "284.3mm", "197.3mm"];
		contents = "This is some text";
		with(TextFramePreference){
			TextColumnCount = 6;
		}
	}
}