StringUtils.lastIndexOfAnyBut() function desired

class StringUtils needs the function lastIndexOfAnyBut()
This would be like indexOfAnyBut() except searches from the end rather than the beginning.
It would be like lastIndexOfAny() except looks for a character other than those in the string rather than for those in the string.

This is the only one of the four combinations of "from beginning"/"from end" and "for any"/"for any but" that is not provided.

Interestingly, the class header doc. mentions "LastIndexOfAnyBut" but the function does not exist - even as a private, as determined by class introspection.

(This is not a frivolous request. I actually did need this function and ended up having to code a search loop.)