Codeigniter Form Dropdown Error After Validation

I'm trying to adapt the form_dropdown to my form in codeigniter. When i'm adding a new page, it doesn't show any errors in parent dropdown section, but after form validation, for instance if user forgets to enter the title label, if its empty or, after validation it gives foreach error in the dropdown section.

I've read that, the second variable must be array and so on for the form_dropdown. But mine is array and not giving any errors in the page before validation. So i can't figure the problem out.

A PHP Error was encountered
Severity: Warning
Message: Invalid argument supplied for foreach()
Filename: helpers/form_helper.php
Line Number: 331

MY_Controller :

class MY_Controller extends CI_Controller{
public $data =  array();

function __construct(){
    parent::__construct();
}
}

Admin Controller :

class Admin_Controller extends MY_Controller{
function __construct(){
    parent::__construct();
    $this->data['meta_title'] = 'My Website Control Panel';
    $this->load->helper('form');
    $this->load->library('form_validation');
    $this->form_validation->set_error_delimiters(' <div class=" alert alert-danger alert-block" ><span class="glyphicon glyphicon glyphicon-minus-sign"></span> ', '<span class="close" data-dismiss="alert">&times;</span></div>');
    $this->load->library('session');
    $this->load->model('user_m');

    $exceptions = array('admin/user/login', 'admin/user/logout');
    if(in_array(uri_string(),$exceptions) == FALSE){
    if($this->user_m->loggedin() == FALSE){
        redirect('admin/user/login');
    }
}
}
}

Controller :

class Page extends Admin_Controller{
public function __construct(){
    parent::__construct();
    $this->load->model('page_m');
}

public function index(){
    $this->data['pages'] = $this->page_m->get_with_parent();
    $this->data['subview'] = "admin/page/index";
    $this->load->view('admin/_layout_main',$this->data);
}

public function edit ($id = NULL)
{
    // Fetch a page or set a new one
    if ($id) {
        $this->data['page'] = $this->page_m->get($id);
        count($this->data['page']) || $this->data['errors'][] = 'Not found.';
    }
    else {
        $this->data['page'] = $this->page_m->get_new();
    }

    // Pages for dropdown
    $this->data['pages_no_parents'] = $this->page_m->get_no_parents();
    // Set up the form
    $rules = $this->page_m->rules;
    $this->form_validation->set_rules($rules);


    // Process the form
    if ($this->form_validation->run() == TRUE) {
        $data = $this->page_m->array_from_post(array('title', 'slug', 'body','keywords','description','parent_id'));
        $this->page_m->save($data, $id);
        redirect('admin/page');
    }
    // Load the view
    $this->data['subview'] = 'admin/page/edit';
    $this->load->view('admin/_layout_main', $this->data);
}
}

Model:

public function get_no_parents ()
{
    // Fetch pages without parents
    $this->db->select('id, title');
    $this->db->where('parent_id', 0);
    $pages = parent::get();

    // Return key => value pair array
    $array = array(
        0 => ''
    );
    if (count($pages)) {
        foreach ($pages as $page) {
            $array[$page->id] = $page->title;
        }
    }

    return $array;
}

View :

<?=form_dropdown('parent_id', $pages_no_parents, set_value('parent_id', $pages_no_parents, $this->input->post('parent_id') ? $this->input->post('parent_id') : $page->parent_id);?>