public Object visit(PropertyIsNull filter,Object extraData){
  LOGGER.finer("exporting NullFilter");
  Expression expr=filter.getExpression();
  expr.accept(this,extraData);
  return extraData;
}

public Object visit ( PropertyIsNull filter , Object extraData ) { LOGGER . finer ( "exporting NullFilter" ) ; Expression expr = filter . getExpression ( ) ; expr . accept ( this , extraData ) ; return extraData ; }
writes the filterbuilder for the null filter .
