[bug-report] inserting link to a target with non-ascii symbols

[Maxim Loginov <zeliboba@mail.ru>]

hi Carsten

I found a bug related to inserting links to the target written in
native language. if I have a header with target like this (in
Russian):

* TODO <<сделать что-то>>

then I want to make a link to this target:
1. C-c l on header (here ok)
2. go to place where to want to make link and C-c C-l 
   (here ok as well, ask for link, insert it, ask for an description) 
3. after description editing or leaving as is RET (oops!)
error appeared:
org-link-escape: Wrong type argument: stringp, nil
this bug is not reproduced if there is no non-ascii chars in target. 
when inserting manually links work perfectly:

[[сделать что-то]]

this bug was introduced recently, did not traced when exactly, before
everything worked fine

best
Maxim