Question about resizing ResizableComponent border?

I fail in modifying border thickness of my documentWindows :

I inherited from one, and add in the constructor :

since resizableBorder is protected.

But I get a crash, pointing to BorderSize constructor.
The same with resizableBorder->setBorderThickness(BorderSize::BorderSize(2, 2, 2, 2));

that border object isn’t supposed to be used directly - the window deletes and re-creates it whenever it needs to.

If you want to change the thickness, override getBorderThickness() or getContentComponentBorder().