Обнаружена ошибка Php. Серьезность: предупреждающее сообщение in_array () ожидает, что параметр 2 будет массивом CODEIGNITER

Я программирую с помощью Codeigniter. У меня ошибка

A Php Error was encountered Severity: Warning Message in_array() expect parameter 2 to be array

Я сравнил код с другим, который работает, но ошибки не обнаружил.

    public function update($post_id)
    {      
        if (!in_array('updatePost', $this->permission)) {
            redirect('dashboard', 'refresh');
        }

        if (!$post_id) {
            redirect('dashboard', 'refresh');
        }

            $data = array(
                'name' => $this->input->post('post_name'),
                'summary' => $this->input->post('summary'),
                'date' => $this->input->post('date'),
                'description' => $this->input->post('description'),
                'subject_id' => json_encode($this->input->post('subjects')),
                'tag_id' => json_encode($this->input->post('tag')),
                'category_id' => $this->input->post('categories'),
                'availability' => $this->input->post('availability'),
            );

            if ($_FILES['post_image']['size'] > 0) {
                $upload_image = $this->upload_image();
                $upload_image = array('image' => $upload_image);

                $this->model_posts->update($upload_image, $post_id);
            }

            $update = $this->model_posts->update($data, $post_id);
            if ($update == true) {
                $this->session->set_flashdata('success', 'Successfully updated');
                redirect('posts/', 'refresh');
            }
            else {
                $this->session->set_flashdata('errors', 'Error occurred!!');
                redirect('posts/update/'.$post_id, 'refresh');
            }
        }
        else {

            $this->data['subjects'] = $this->model_subjects->getActiveSubjects();         
            $this->data['tag'] = $this->model_tag->getActiveTag();           
            $this->data['categories'] = $this->model_categories->getActiveCategory();          

            $post_data = $this->model_posts->getPostData($post_id);
            $this->data['post_data'] = $post_data;
            $this->render_template('posts/edit', $this->data); 
        }   
    }

edit // Форма публикации

<div class = "form-group">
                  <label for = "tag">Tag</label>
                  <?php $tag_data = json_decode($post_data['tag_id']); ?>
                  <select class = "form-control select_group" id = "tag" name = "tag[]" multiple = "multiple">
                    <?php foreach ($tag as $k => $v): ?>
                      <option value = "<?php echo $v['id'] ?>" <?php if (in_array($v['id'], $tag_data)) { echo 'selected = "selected"'; } ?>><?php echo $v['name'] ?></option>
                    <?php endforeach ?>
                  </select>
                </div>