asp.net mvc - Model binder does not convert json to IEnumerable<T> -

i sending json data controller action via jquery ajax post. ienumerable in action alway null.

is json wrong or why model binder not convert json ienumerable ?

public actionresult update(ienumerable<teststep> teststeps) {    // }  $.ajax({             url: '@url.action("update", "teststep")',             type: 'post',             data: [{ "errortext": "oh bad happended.", "unitid": "10" }, { "errortext": "you got man.", "unitid": "20"}],             success: function (response) {                 debugger;                 if (response.success) {                     dlg.dialog("close");                     // update ui                  }                 else {                     // reload dialog form show model/validation errors                      dlg.html(response);                 }             }         });  public class teststep {   [hiddeninput(displayvalue = false)]  public int unitid { get; set; }       public string errortext { get; set; }     // other props removed readability     } 

in order collections (arrays, ienumerables, etc) pass correctly through modelbinder action method, i've had set traditional: true option on ajax call:

$.ajax({     url: '@url.action("update", "teststep")',     type: 'post',     traditional: true,     ...