Add extension only to files without one

[brianholt2]

Is it possible to add extensions only to those files currently without one, using any of the filter or other options?
I've tried but haven't figured a way of successfully identifying only those files from a list of sub-folders without a file extension.
Grateful for any help / support

[therube]

Everything.
Use its function, ext:
(Normally something like, ext:mp4, to find .mp4 files, but if you put nothing there, ext:, it finds files without extensions.)
Drag wanted files into BRU.