How to make update statement to work

I want to nullify fields which does not exist in reference table.
I tried

UPDATE demo.toode       SET "liik"=NULL,            "grupp"=NULL      WHERE ("grupp",        "liik") NOT IN
(SELECT("grupp",          "liik") FROM          "artliik")
 

but this causes error:


ERROR:  operator does not exist: character = record
HINT:  No operator matches the given name and argument type(s). You may need 
to add explicit type casts.


How to write this UPDATE statement properly ?