Hello,

The string-trim-* functions earned a new optional argument in this commit[1]. I realized that was the case when my package using string-trim-right with 2 arguments failed on emacs 25 and older.

[1]: http://git.savannah.gnu.org/cgit/emacs.git/commit/?h=emacs-26&id=c189986b241cbe79b0e027fa08bba710ac645bb3