title: Kendo DropDownList requestEnd push value undefined
body: <p>I have a DropDownList initialize via the data- attributes. I need to add an item to the list but the code I'm using displays the value as 'undefined' after I push the new option.</p>
  
  <p>Here is my element using the data- attributes (works fine):</p>
  
  <pre><code> &lt;select id="#people_list"
       name="person_id"
       class="form-control"
       data-role="dropdownlist"
       data-source="datasource_people"
       data-option-label="Select A Name"
       data-auto-bind="true"
       data-text-field="name"
       data-value-Field="name"
       data-ignore-case="true"
       data-filter="startswith"
       &gt;
       &lt;/select&gt;
  </code></pre>
  
  <p>Here is my datasource params (works fine):</p>
  
  <pre><code>datasource_people = new kendo.data.DataSource({
          type: "json",
          serverFiltering: true,
          transport: {
              read: {
                  dataType: 'json',
                  type: 'GET',
                  url: '/restful/people/'
              }
          },
          filter: {
              field: "status",
              operator: "eq",
              value: 1
          },
          schema: {
              data: function(response) {
                  return response.data.people;
              },
              model: {
                  id: "person_id",
                  fields: {
                      person_id: {type: "number"},
                      name: { type: "string"}
                  }
              },
              errors: "error",
              total: function(response) {
                  return response.data.total;
              }
          }
      });
  </code></pre>
  
  <p>Then Later (doesn't work - adds new item as 'undefined'):</p>
  
  <pre><code>$("#people_list").kendoDropDownList({
      dataTextField: "text",
      dataValueField: "value",
      dataSource: {
          datasource_people,
          requestEnd: function (e) {
              e.response.push({text: "John", value: "John"});
          }
      }
  });
  </code></pre>