Validate Select2

I have a question

How these fields(select2) are validated?

I get an error because it is required and does not send any value

This is my form





				 <?php 

						echo CHtml::hiddenField('Id_Usuario','', array('class' => ''));  					

				        $this->widget('ext.select2.ESelect2',array(

				           'selector' => '#Id_Usuario',

				           'model'=>$model,

				           'attribute' => 'Id_Usuario',

				         //  'value'=>$model->Id_Usuario,				    

				           'options'  => array(				            

					           'allowClear'=>true,				           

					           'placeholder'=>'Selecione el Demandante',	

					           'width' => '220px',			         

					           'ajax'=>array(

						           'url'=>$this->createUrl('ListarDemandantes'),

						           'dataType' => 'json',

						      //    'type'=>'GET',

						           'quietMillis'=> 100,

						           'data' => 'js: function(text,page) {

						            return {					                       

						                        q: text, 

						                        page_limit: 10,

						                        page: page,

						                    };

						                }',


						            'results'=>'js:function(data,page) { var more = (page * 10) < data.total; return {results: data, more:more };

						            

						             }',

						              

	                               'formatSelection'=>'js: function(data) {

	                                    return data.title;

	                                }',

	                               'initSelection'=>'js: function(element, callback) {

	                                    var elementText = $(element).data("init-text");

	                                    callback({"title":elementText});

	                               }',

					        ),					             

				       ),				         

				    ));

				 ?>




My controller




	public function actionListarDemandantes(){

         

               $lista =Usuarios::model()->findAll('Nombres like :term or Apellidos like :term' ,array(':term'=>"%".$_GET['q']."%"));

               $reusultados = array();

               foreach ($lista as $model){

      		     $reusultados[] = array(          			 	

                    'id'=>$model->Id_Usuario,                        

                    'text'=>$model->Nombres.' '.$model->Apellidos,

      	 ); 

    	}

            echo CJSON::encode($reusultados);                       

    }



Thank you very much