[jQuery] Validate selectedValue in a combobox

[ciupaz]

Hi all,
I have a simple combobox like this:

<form id="myForm" action="" method="post">
<select id="city">
                    <option value="">Select a city</option>
                    <option value="1">Milan</option>
                    <option value="2">Turin</option>
                    <option value="3">Rome</option>
                    <option value="4">Venice</option>
</select>
</form>


and a validation rule like this:

$('form#myForm').validate({
            rules: {
                city: {
                    required: true
                }
            },
            messages: {
                city: {
                    required: "<span style='color:#ff0000;'>Please,
select a city</span>"
                }
            }
        });

The problem is that doesn't work!
Where I've wrong?

Thanks a lot.

Luis