No result appear in the autocomplete - jquery-ui

Question

The action return a JSonResult and the content is correct. I missed something in the autocomplete code ?
HTML :
<input type="text" class="span12" id="mytextbox" />
The javascript :
<script>
$(document).ready(function () {
$("#mytextbox").autocomplete({
minLength: 2,
source: function(request,response) {
$.ajax({
url: "MyController/MyAction",
type: "POST",
dataType: "json",
data: { term: request.term },
success: function (data) {
response($.map(data, function (item) {
return { firstname: item.FirstName, lastname: item.LastName, code: item.Code };
}))
}
})
},
messages: {
noResults: "", results: ""
}
})
.data("ui-autocomplete")._renderItem = function (ul, item) {
return $("<li>")
.append("<a>" + item.firstname + "<br>" + item.lastname + "</a>")
.appendTo(ul);
};
})
</script>

Answer 1

The next code works, where availableTags replace your ajax.
<script>
$(document).ready(function () {
var availableTags = [
"ActionScript",
"AppleScript",
"Asp",
"BASIC"];
$("#mytextbox").autocomplete({
minLength: 2,
source: availableTags,
messages: {
noResults: "", results: ""
}
}).data("ui-autocomplete").renderItem = function (ul, item) {
return $("<li>")
.append("<a>" + item.firstname + "<br>" + item.lastname + "</a>")
.appendTo(ul);
};
});
</script>
This might be helpful: http://api.jquery.com/jQuery.data/#jQuery-data-element
Update:
The problem is this line:
.data("ui-autocomplete").renderItem = function (ul, item) {
you got
.data("ui-autocomplete").**_**renderItem = function (ul, item) {