File_Picker in appex mode: expand/collapse folder button image is None

[cvp]

@omz When I use your File_Picker in appex mode, the image of the expand/collapse folder button is None, but the button is active and does its work.

Other built-in images used as here-after and button image is displayed, but why?

if not appex.is_running_extension():					
	btn = ui.Button(image=ui.Image.named('CollapseFolder' if has_children else 'ExpandFolder'))
else:
	btn = ui.Button(image=ui.Image.named('iob:arrow_down_b_24' if has_children else 'iob:arrow_right_b_24'))

Bug?