Syntax error at or near "EXCEPTION"

Question

Could anybody tell me where possibly can I have syntax error in trigger procedure below?

CREATE OR REPLACE FUNCTION hd.insert_insteadof_update()
  RETURNS trigger AS
$BODY$
 BEGIN                                         

   IF (OLD <> NEW)                               
   THEN
     NEW.set_date = now();         

     INSERT INTO hd.ticket_attachment              
     VALUES (NEW.*);

   EXCEPTION WHEN UNIQUE_VIOLATION THEN END;  
   END IF;      

   RETURN NULL;  

 END;   
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;

I use PostgreSQL 8.4.

ERROR: syntax error at or near "EXCEPTION" LINE 13: EXCEPTION WHEN UNIQUE_VIOLATION THEN END;
^

********** Error **********

ERROR: syntax error at or near "EXCEPTION" SQL state: 42601 Character: 356