when no widgets are added to the sidebar, there will be a default loaded.
(that's typical wordpress style by the way).
WHY would you like to have a blank sidebar??
...an idea would be to add just a text widget and leave it blank.
but you will still have a blank widget title left then.
changing the theme files just for this is not a good idea, as you would not be update safe anymore.
making a child theme just for that would be too much effort just for such a thing..
anyway, you can just use full width layout or set responsive = disabled and then define for example a very small website width like 600px and use full width template..
what are you trying to achieve?
...really curious, i don't understand blank sidebars. :-?