asp.net core getJSON data to javascript not working

I have a div id=title and input id=titleArea. I want to check if titleArea content exists before posting. I tried with getJSON but I understood I cannot get boolean values so I am getting string. emptu or not empty. The id is sent from script, I've checked that but no data is received

View script

<script>
        $("#title").on('change', function () {
            var id = $("#titleArea").val();
            var msg = "";
            $.getJSON(`?handler=CheckTitle&id=${id}`, (data) => {
                if (jQuery.isEmptyObject(data)) {
                    $("#btnSubmit").attr("disabled", true)
                }
                else {
                    $("#btnSubmit").attr("disabled", false)
                }
            });
        });
        
    </script>

JSON

public async Task<JsonResult> OnGetCheckTitle(string id)
        {
            var checkTitle = await _context.BlogDatas.Where(s => s.Title == id).Select(s => s.BID).SingleOrDefaultAsync();

            return new JsonResult(checkTitle);
        }