剑道工具提示为空

dI use a kendo tooltip on cells of a column of a kendo grid but the content of the tooltip is empty. When I use the chrome debugger, values are correctly set but there is nothing in my tooltip.

    $("#gri").kendoTooltip({
        filter: "span.tooltip",
        position: "right",
        content: function (e) {
            var tooltipHtml;
            $.ajax({
                url: ".." + appBaseUrl + "api/Infobulle?id=" + $(e.target[0]).attr("id"),
                contentType: "application/json",
                dataType: "json",
                data: {},
                type: "GET",
                async: false
            }).done(function (data) {   // data.Result is a JSON object from the server with details for the row
                if (!data.HasErrors) {
                    var result = data.Data;
                    tooltipHtml = "Identifiant : " + result.identifiant;
                } else {
                    tooltipHtml = "Une erreur est survenue";
                }
                // set tooltip content here (done callback of the ajax req)
                e.sender.content.html(tooltipHtml);
            });
        }

Any idea ? Why it is empty ?

After looking at the dev's answer on telerik forums, i found out that you need to do something like

content: function(){
   var result = "";
   $.ajax({url: "https://jsonplaceholder.typicode.com/todos/1", async:false , success: function(response){
        result = response.title
   }});
   return result;
}

changing directly with e.sender.content.html() won't work, instead we have to return the value. And i tried several approach :

1. i tried mimick ajax call with setTimeOut, returning string inside it or using e.sender.content.html() wont work
2. i tried to use content.url ( the only minus i still don't know how to modify the response, i display the whole response)
3. the third one i tried to use the dev's answer from here

AND check my example in dojo for working example, hover over the third try