在ajax中的错误没有被击中

I am using ajax to send values from my view to a controller in my application.

Ajax:

<script type="text/javascript">
$('#SendToController').on('click', function() {
    sendToController();
    return false;
});
function sendToController(){
    var selectedM = $('#Month').val();
    var chosenY = $('#Year').val();
    var chosenC = $('#County').val();
    //alert(chosenY);

    $.ajax({
        url: '/ALog/MReports/Generate',
        data: { 'monthV' : selectedM, 'year' : chosenY, 'county' : chosenC },
        type: 'GET',
        cache: false,
        success: function (data) {
            $("body").html(data);
            $('.dropdown-toggle').dropdown();
        },
        error: function () {
            if (selectedM === "") {
                alert("Error 1!");
            }
            else if (chosenY === "") {
                alert("Error 2!");
            }
            else if (chosenC === "") {
                alert("Error 3!");
            }
        }
    });
}


</script>

Now, on my form i have 3 dropdownlists which I am getting the values from in the ajax code above. The only time the ajax function goes to the error part is if chosenC and/or selectedM is empty, but if chosenY is empty it still goes to success.

I have alerted the value of chosenY when I left it blank to ensure that I am checking for the right value with javascript, either null or empty ("").. I have tried both, and neither work..

Here is the result from when I alerted the chosenY

so from that I thought it was an empty string.. so I am checking for that.. but it doesn't matter because even if it is empty the ajax method is considering that as a success and not an error.. why is that?

Any help is appreciated.

Thanks to @MarcB I figured this out. It was in fact on the server side, and it wasn't throwing an error because it was using that value to search for records in the database table even though it was empty string.

So i just converted the string to an int which would throw an exception if year is passed as an empty string.

Thanks again for the ideas/help!