Any chance to fix this ?
I don't think this is something that should be "fixed"... Child gadgets (such as buttons, labels, textfields, panels and canvases) require a parent for them to be displayed. If the old MaxGUI driver allowed for this not to be the case then it shouldn't have as it almost certainly won't work cross-platform.
Not that I should be encouraging MaxGUI mal-practice, but if you are really stuck, try substituting Desktop() in instead of Null as the parent parameter but I have no idea if this will work as intended. ;-)