[Vala] error on property.

[Alexey Lubimov <avl l14 ru>]

public class Info.PersonInfo {
 public string f_name;
 public string m_name;
 public string l_name;
 public string fio  {get {return this.get_fio();}}

 public string get_fio() {
   return "%s %C. %C".printf(l_name,f_name.get_char(),m_name.get_char());
 }
}



PersonInfo.vala:12.7-12.28: error: Return value transfers ownership but 
method return type hasn't been declared to transfer ownership

That's wrong?
any tips?