Whats the error? Stating that there is an error is not helpful if you don't include the error text.
i cant help troubleshoot an error if i don't what the error says.
perhaps if you send a link a link to your page where i can see the problem i can help you fix it.
the idea is not to add a keyword hidden element.
the idea is to modify the code to use the elements in your search form.
you have a search form that has an element in it. If that element is left blank you want no results to be found...
ok, so what is the name of the element inn your form?
the example uses an element named keyword, you need to change keyword to whatever is used for your form element name.