Clear dropdownlist with JQuery

I wrote this little function to fill a drop down list with data from the server.

function fillDropDown(url, dropdown) {
    $.ajax({
        url: url,
        dataType: "json"
    }).done(function (data) {
        // Clear drop down list
        $(dropdown).find("option").remove(); <<<<<< Issue here
        // Fill drop down list with new data
        $(data).each(function () {
            // Create option
            var $option = $("<option />");
            // Add value and text to option
            $option.attr("value", this.value).text(this.text);
            // Add option to drop down list
            $(dropdown).append($option);
        });
    });
}

I can then call the function in this way:

fillDropDown("/someurl/getdata", $("#dropdownbox1"))

Everything is working perfectly, except for the one line where I'm clearing old data from the drop down list. What am I doing wrong?

Any tips that might help to improve this code are also highly appreciated.