เช็คค่าว่างของ file ที่อัพโหลดครับ ผมอยากรู้ว่าถ้าจะเช็คค่า วางของ type ="file" ต้องเขียน if else อย่างไร

$id             = $this->input->post("id");
            $title          = $this->input->post("title");
            $description    = $this->input->post("description"); 
            $url            = $this->input->post("url");
            $file_name      = $this->input->post("file_name");

            $this->load->library('upload');
            $config['upload_path'] = './uploads/member';

            $config['allowed_types'] = 'gif|jpg|png|jpeg|mp4';
            $config['max_size']     = '102400';
            $config['max_width'] = '10000';
            $config['max_height'] = '10000';
            $name_file = "uploads-".time();
            $config['file_name'] = $name_file;

            // print_r($config['upload_path']);

            // Alternately you can set preferences by calling the ``initialize()`` method. Useful if you auto-load the class:
            $this->upload->initialize($config);

             $editdata = array();
                
                if(empty($file_name))
                {
                    $editdata = array( 
                                       
                                        'title'         => $title,
                                        'description'   => $description,
                                        // 'file_name'     => $gamber['file_name'],
                                        'url'           => $url,
                                        'update_at'    =>  date("Y-m-d H:i:s")
                                    );
                                               
                }
                else
                {
                    if ($_FILES['file_name']['name']) {           
                        $field_name = 'file_name';
                        if ($this->upload->do_upload('file_name')){

                    $gamber     = $this->upload->data();
                    $editdata   = array( 
                                        'title'         => $title,
                                        'description'   => $description,
                                        'file_name'     => $gamber['file_name'],
                                        'url'           => $url,
                                        'update_at'    =>  date("Y-m-d H:i:s")
                                     );
                        }
                    }
                }
                                    $this->db->where('id', $id);
                                    $resultsedit = $this->db->update('tbl_member',$editdata);
                                  

                                    if($resultsedit > 0)
                                    {
                                        $this->session->set_flashdata('success', 'successly');
                                    }
                                    else
                                    {
                                        $this->session->set_flashdata('error', 'failed');
                                    }
                               
                                    redirect('member');