public void addArgument(AstNode arg){
  assertNotNull(arg);
  if (arguments == null) {
    arguments=new ArrayList<AstNode>();
  }
  arguments.add(arg);
  arg.setParent(this);
}

public void addArgument ( AstNode arg ) { assertNotNull ( arg ) ; if ( arguments == null ) { arguments = new ArrayList < AstNode > ( ) ; } arguments . add ( arg ) ; arg . setParent ( this ) ; }
adds an argument to the list , and sets its parent to this node .
