Lack of selecting capacity with if statement / append method - jquery-ui

Question

I want to propose an autocomplete list (jquery ui 1.8) with some words in bold font.
The JSON source looks like :
{"especes":[{"fk_sp":number,"nom_espece":name,"nom_valide":0 or 1}].
My script is like that :
$(function(){
$('#id').autocomplete({
source: function(request, response) {
$.getJSON("fichier.php", {
term: request.term
}, function(data) {
var array = data.error ? [] : $.map(data.especes, function(m) {
return {
label: m.nom_espece,
value: m.fk_sp,
valid: m.nom_valide
};
});
response(array);
});
},
select: function (event, ui) {
$("#espece").val(ui.item.label);
$("#fk_sp").val(ui.item.value);
}
}).data( "ui-autocomplete" )._renderItem = function( ul, item ) {
return $( "<li></li>" )
.data( "item.autocomplete", item )
.append( item.valid == '1' ? "<b>" + item.label + "</b>" : item.label)
.appendTo( ul );
};
});
If I use :
.data( "ui-autocomplete" ) => I have the good selectable list without the bold lines,
.data( "ui-Autocomplete" ) ou .data( "uiAutocomplete" ) => nothing works,
and if I juste write ._renderItem without .data( "ui-autocomplete" ) => I have a pretty list with the good names in bold, but I can't select any name of the list !
I don't find where is my error (I suppose it is somwhere with the "select :" part).