Nahravanie suboru - codeigniter

function upload_img()
   {
      // nastavenie upload obrazku
      $error ='';
      $config['upload_path'] = './assets/img/users/';
      $config['allowed_types'] = 'gif|jpg|png|jpeg';
      $this->load->library('upload', $config);

      // ak sa stala nejaka chyba
      if ( ! $this->upload->do_upload())
      {
          $error = array('error' => $this->upload->display_errors());
          $this->session->set_flashdata('message', $error['error']);
      }
      else
      {
         
          // upne data do ftp
          $data = array('upload_data' => $this->upload->data());
          // resize imageeee and redirect powa
          $img_cfg_thumb['image_library'] = 'gd2';
          $img_cfg_thumb['source_image'] = $data['upload_data']['full_path'];
          $img_cfg_thumb['maintain_ratio'] = true;
          $img_cfg_thumb['master_dim'] = 'width';
          $img_cfg_thumb['height'] = 338;
          $img_cfg_thumb['width'] = 600;
          $this->load->library('image_lib');
          $this->image_lib->initialize($img_cfg_thumb);
          $this->image_lib->resize();
          // prepise subor novym
          $data = array('upload_data' => $this->upload->data());

      }
   }

var_dump(is_dir('./assets/img/users/'));

The upload path does not appear to be valid.