/**
  * register a class indicated by name
  *
  * @param kryo
  * @param s name of a class - might not exist
  * @param handled Set of classes already handles
  */
 protected void doRegistration(@Nonnull Kryo kryo, @Nonnull String s) {
   Class c;
   try {
     c = Class.forName(s);
     doRegistration(kryo, c);
   } catch (ClassNotFoundException e) {
     return;
   }
 }