session userdata has null initials, is not inputted into the database - codeigniter

Question

I have a code like this, the problem is when I input why the id_user value is "0".
even though the admin logged in is "1"
Is there anything missing in my script code?
Controller
public function tambah() {
// $this->session->set_userdata('upload_image_file_manager',true);
$kategori = $this->kategori_m->tampil();
$this->session->set_userdata('upload_image_file_manager',true);
// Validasi
$valid = $this->form_validation;
$valid->set_rules('judul_berita','Judul','required',
array( 'required' => 'Judul harus diisi'));
$valid->set_rules('isi_berita','Isi','required',
array( 'required' => 'Isi berita harus diisi'));
if($valid->run()) {
if(!empty($_FILES['gambar']['name'])) {
$config['upload_path'] = './resch/dev/admin/assets/media/';
$config['allowed_types'] = 'gif|jpg|png|svg|jpeg';
$config['max_size'] = '20480'; // 2 Mb
$this->load->library('upload', $config);
if(! $this->upload->do_upload('gambar')) {
// End validasi
$data = array( 'head_title' => 'Berita- Edutech Solution',
'title' => 'Tambah Berita',
'head_menu' => 'Berita',
'sub_title' => 'Total Berita',
'kategori' => $kategori,
'error' => $this->upload->display_errors(),
'isi' => 'superadmin/berita/tambah');
$this->load->view('superadmin/template/wrapper_admin', $data, FALSE);
// Masuk database
}else{
$upload_data = array('uploads' =>$this->upload->data());
// Image Editor
$config['image_library'] = 'gd2';
$config['source_image'] = './resch/dev/admin/assets/media/'.$upload_data['uploads']['file_name'];
$config['new_image'] = './resch/dev/admin/assets/media/thumbs';
$config['create_thumb'] = TRUE;
$config['quality'] = "100%";
$config['maintain_ratio'] = TRUE;
$config['width'] = 360; // Pixel
$config['height'] = 360; // Pixel
$config['x_axis'] = 0;
$config['y_axis'] = 0;
$config['thumb_marker'] = '';
$this->load->library('image_lib', $config);
$this->image_lib->resize();
$i = $this->input;
$slug = url_title($i->post('judul_berita'),'dash',TRUE);
$data = array( 'id_kategori' => $i->post('id_kategori'),
'id_user' => $this->session->userdata('user_name'),
'slug_berita' => $slug,
'judul_berita' => $i->post('judul_berita'),
'isi_berita' => $i->post('isi_berita'),
'jenis_berita' => $i->post('jenis_berita'),
'status_berita' => $i->post('status_berita'),
'gambar' => $upload_data['uploads']['file_name'],
// 'icon' => $i->post('icon'),
'keyword' => $i->post('keyword'),
'tanggal_publish'=> date('Y-m-d',strtotime($i->post('tanggal_publish'))).' '.$i->post('jam_publish'),
// 'tanggal_mulai' => $i->post('tanggal_mulai'),
// 'tanggal_selesai' => $i->post('tanggal_selesai'),
// 'urutan' => $i->post('urutan'),
'tanggal_post' => date('Y-m-d H:i:s'),
);
$this->berita_m->tambah($data);
$this->session->set_flashdata('sukses', 'Data telah ditambah');
redirect(base_url('superadmin/berita/jenis_berita/'.$i->post('jenis_berita')),'refresh');
}}else{
$i = $this->input;
$slug = url_title($i->post('judul_berita'),'dash',TRUE);
$data = array( 'id_kategori' => $i->post('id_kategori'),
'id_user' => $this->session->userdata('user_name'),
'slug_berita' => $slug,
'judul_berita' => $i->post('judul_berita'),
'isi_berita' => $i->post('isi_berita'),
'jenis_berita' => $i->post('jenis_berita'),
'status_berita' => $i->post('status_berita'),
'gambar' => $upload_data['uploads']['file_name'],
// 'icon' => $i->post('icon'),
'keyword' => $i->post('keyword'),
'tanggal_publish'=> date('Y-m-d',strtotime($i->post('tanggal_publish'))).' '.$i->post('jam_publish'),
// 'tanggal_mulai' => $i->post('tanggal_mulai'),
// 'tanggal_selesai' => $i->post('tanggal_selesai'),
// 'urutan' => $i->post('urutan'),
'tanggal_post' => date('Y-m-d H:i:s'),
);
$this->berita_m->tambah($data);
$this->session->set_flashdata('sukses', 'Data telah ditambah');
redirect(base_url('superadmin/berita/jenis_berita/'.$i->post('jenis_berita')),'refresh');
}}
// End masuk database
$data = array( 'head_title' => 'Berita- Edutech Solution',
'title' => 'Tambah Berita',
'head_menu' => 'Berita',
'sub_title' => 'Total Berita',
'kategori' => $kategori,
'isi' => 'superadmin/berita/tambah');
$this->load->view('superadmin/template/wrapper_admin', $data, FALSE);
}
in a model like this, I feel there is no problem
Model
public function tampil() {
$this->db->select('berita.*, user.nama, kategori.nama_kategori, kategori.slug_kategori');
$this->db->from('berita');
// Join dg 2 tabel
$this->db->join('kategori','kategori.id_kategori = berita.id_kategori','LEFT');
$this->db->join('user','user.id_user = berita.id_user','LEFT');
// End join
$this->db->order_by('id_berita','DESC');
$query = $this->db->get();
return $query->result();
}
// Tambah
public function tambah($data) {
$this->db->insert('berita',$data);
}
session userdata has null initials, not inputted to the database and
because I was confused, I skip. and create a function to update, but when the update function is executed it will give an error "too few arguments to functio"
I don't understand the problem.