public void addUser(PrincipalUser user){
  SystemAssert.requireArgument(user != null,"Null user can not be added.");
  users.add(user);
}

public void addUser ( PrincipalUser user ) { SystemAssert . requireArgument ( user != null , "Null user can not be added." ) ; users . add ( user ) ; }
adds an authorized user of the namespace .
