FormatException in DetailsView, which uses dynamically inserted value for Item of DrodDownList

Question

Hello!

I use DetailsView with ObjectDataSource to insert entry in database. DropDownList ddl_kinds is bound to some field. I complete dropdownlist dynamically. Last listItem of dropdownlist has TextField "Null value" and ValueField "0". But when I choose this item in DetailsView and try to send form, FormatException is thrown.

There is one strange moment. I complete dropdownlist dynamically in js-function after using web service. There is code.

//Variable 'result' is result of web service. Result is array of items.
//Every item has string-field 'Name' and int-field 'Kind_id'.
function Kind_success(result){    
    var ddl_select = document.getElementById("ddl_kinds");
    ddl_select.innerHTML = "";        
    for (var n = 0; n < result.length; n++){
        var option = document.createElement("option");
        option.value = result[n].Kind_id;
        option.innerHTML = result[n].Name;
        ddl_select.appendChild(option);
    }

    // inserting null-item in dropdownlist
    var null_option = document.createElement("option");
    null_option.value = 0;
    null_option.innerHTML = "Null value";
    ddl_select.appendChild(null_option);
}

Web service returns result with two items. First has Kind_id 2, second has Kind_id 3. If I use any value for null_option, except 2 or 3, FormatException is thrown too. But it isn't trrown, if I use value 2 or 3 for null_option.Value.

Is there any way to correctly use null-option?