jquery autocomplete shows nothing

for several days I have the problem, that when I call the jquery autocomplete function it does not show me anything, and I have already reviewed the questions that others have already formulated, but I still do not realize what the problem is, I suppose that because I am not very clear JavaScript. Thanks in advance to anyone who can help me out!

The function is working, in fact I have tried to follow it with the debugger and it seems to work. In my view, a JSP page, I have this code:

<script language="javascript" type="text/javascript">
        $(function () {
            $("#cuenta").autocomplete({
                source: function (request, response) {
                    alert("pepe");
                    $.ajax({
                        type: "POST",
                        url: "CuentaBusca",
                        contentType: "application/json; charset=utf-8",
                        dataType: "json",
                        minLength: 2,
                        delay: 100,
                        success: function (data) {
                            console.log( data);
                            response(data);
                        },
                        select: function (event, ui) {
                            return false;
                        }
                    });
                }
            });
        });
    </script>

The console.log shows me the following output:

And in the servlet I have the following code, which also works:

  protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
     PrintWriter out = response.getWriter();


    DBConexion conex = null;
    try {
        conex = new DBConexion();
    } catch (SQLException ex) {
        throw new ServletException("Sucedio un Error al Realizar la Conexion a la Base de Datos !", ex);
    }

    Connection conn = conex.getConexion();

    try {

        PreparedStatement ps = conn.prepareStatement("select id,nombre from cuentas order by nombre");
        ResultSet rs = ps.executeQuery();

        JsonObject json_response = new JsonObject();
        JsonArray data_json = new JsonArray();

        while (rs.next()) {
            JsonObject json = new JsonObject();

            json.addProperty("id", rs.getInt("id"));
            json.addProperty("nombre", rs.getString("nombre"));
            data_json.add(json);
        }
        json_response.add("aaData", data_json);

        response.setContentType("application/Json");
        response.getWriter().write(json_response.toString());

    } catch (SQLException ex) {
        throw new ServletException("Sucedio un Error al Realizar la Conexion a la Base de Datos !", ex);

    }

    // Cierra la Conexion 
    try {
        conex.closeConexion();
    } catch (SQLException ex) {
        throw new ServletException("Sucedio un Error al Cerrar la Conexion en la Base de Datos !", ex);
    }
}

I suspect that I am returning in the wrong format from the servlet, but I couldn't find a clearer explanation. Any ideas?

Regards, Ferdinand