Magento 1.9 Grid – Issue in Grid Serialization

In Tabs.php

 $this->addTab('form', array(
        'label' => Mage::helper('example')->__('Select Person'),
        'url' => $this->getUrl('*/*/person', array('_current' => true)),
        'class' => 'ajax',
    ));

Controller

public function personAction(){
    $this->loadLayout();
    $this->getLayout()->getBlock('person.grid')
    ->setProducts($this->getRequest()->getPost('persons', null));
    $this->renderLayout();
}


public function persongridAction(){
    $this->loadLayout();
    $this->getLayout()->getBlock('person.grid')
    ->setProducts($this->getRequest()->getPost('persons', null));
    $this->renderLayout();
}

in xml file

<example_adminhtml_select_person>

   <block type="core/text_list" name="root" output="toHtml">
       <block type="tuition/adminhtml_student_edit_tab_grid" name="person.grid"/>
       <block type="adminhtml/widget_grid_serializer" name="grid_serializer">
           <reference name="grid_serializer">
               <action method="initSerializerBlock">
                   <grid_block_name>person.grid</grid_block_name>
                   <data_callback>getSelectedPersons</data_callback>
                   <hidden_input_name>persons</hidden_input_name>
                   <reload_param_name>persons</reload_param_name>
               </action>

           </reference>
       </block>
   </block>

<example_adminhtml_select_persongrid>
    <block type="core/text_list" name="root" output="toHtml">
        <block type="example/adminhtml_example_edit_tab_grid" name="person.grid"/>
    </block>
</example_adminhtml_select_persongrid>

Grid.php

<?php
 class Company_Example_Block_Adminhtml_Example_Edit_Tab_Grid extends     Mage_Adminhtml_Block_Widget_Grid
{
 public function __construct()
 {
    parent::__construct();
    $this->setId('personGrid');
    $this->setUseAjax(false); // Using ajax grid is important
    $this->setDefaultSort('person_id');
    $this->setDefaultFilter(array('person'=>'')); // By default we have added a filter for the rows, that in_products value to be 1
    $this->setSaveParametersInSession(false);  //Dont save paramters in session or else it creates problems
}

protected function _prepareColumns() {

    $this->addColumn('person_id', array(
        'header_css_class'  => 'a-center',
        'header'    => $this->__('Select'),
        'required'          => 1,
        'type'              => 'checkbox',
        'html_name'         => 'person_id',
        'values'            => $this->_getSelectedPersons(),
        'align'             => 'center',
        'index'             => 'person_id'
    ));


    $this->addColumn('person_name', array(
        'header'=> Mage::helper('example')->__('Name'),
        'align' => 'left',
        'index' => 'name',
    ));



    return parent::_prepareColumns();
}

protected function _getSelectedPersons()   // Used in grid to return selected customers values.
{
    $person = array_keys($this->getSelectedPersons());
    return $person;
}
protected function _prepareCollection() {
    $currentStudentId = $this->getRequest()->getParam('id');
    $collection = Mage::getModel('example/person')->getCollection()
                ->addFieldToFilter('student_ids',array('finset' => $currentStudentId));
    $this->setCollection($collection);
    return parent::_prepareCollection();
}
public function getSelectedTutors()
{
    // Customer Data
    $tm_id = $this->getRequest()->getParam('id');
    if(!isset($tm_id)) {
        $tm_id = 0;
    }
    $conn = Mage::getModel('example/person')->load($tm_id);
    $data =  $conn->getData('person_id');
    $datas = explode(',',$data);


    $persons = $datas; 

    // This is hard-coded right now, but should actually get values from database.
    $tutIds = array();

    foreach($persons as $person) {

            $tutIds[$person] = array('id'=>$person);

    }

    return $tutIds;
}


public function getGridUrl()
{
    return $this->_getData('grid_url') ? $this->_getData('grid_url') : $this->getUrl('*/*/persongrid', array('_current'=>true));
}

protected function _addColumnFilterToCollection($column)
{

    if ($column->getId() == 'person') {
        $personIds = $this->_getSelectedPersons();
        if (empty($personIds)) {
            $personIds = 0;
        }
        if ($column->getFilter()->getValue()) {
            $this->getCollection()->addFieldToFilter('person_id', array('in'=>$personIds));
        } else {
            if($personIds) {
                $this->getCollection()->addFieldToFilter('person_id', array('nin'=>$personIds));
            }
        }
    } else {
        parent::_addColumnFilterToCollection($column);
    }
    return $this;
}

}?>

This is my code for grid serializer. My problem is When i am select grid and save in database and if i m edit that form that time checkbox is selected but if i m save that edit form i m getting null value of that because in hidden input i m not getting database value

See here

If i want that value again i have to unselect that checkbox and again i want to select that checkbox than i m getting value but i dont want to do this. I want database value in that input hidden

input hidden

<input type="hidden" name="persons" value="" id="id_6109c7e4877a7d469e1cc8b962055949">

How to solve this problem