For example, when downloading images from Twitter they save without a file extension, so I fix them all to .jpg. At the moment, I have a really long filter excluding all known file types, then apply the fix.
Filters(12) would need a checkmark for "Regex" and without the checkmark for "Folders". Then a "Mask" like ^([^.]+|.*\.)$ could show any names with no-dots or dots at the very-end. BRU cannot rename any files ending with a dot, but they can be removed on the command-line.