unknown property error

News.php

<?php

namespace common\modules\news\models;

use common\modules\backend\components\behaviors\UploadImageBehavior;
use himiklab\sortablegrid\SortableGridBehavior;
use Yii;
use common\modules\user\models\User;
use common\modules\category\models\Category;
use yii\behaviors\TimestampBehavior;
use yii\db\Expression;

/**
 * This is the model class for table "{{%news}}".
 *
 * @property int $id
 * @property int $category_id
 * @property string $title
 * @property string $slug
 * @property string $short_text
 * @property string $full_text
 * @property string $image
 * @property string $created_at
 * @property string $updated_at
 * @property int $sort
 * @property int $status
 * @property string $lang
 *
 * @property User $updatedBy
 * @property User $updated_by
 * @property Category $category
 * @property User $created_by
 */
class News extends \yii\db\ActiveRecord
{
    const STATUS_DISABLED = 0;
    const STATUS_ACTIVE = 1;

  // WARNING: если не вставить эти 2 переменные - возникает ошибка
    public $created_by;
    public $updated_by;

    /**
     * @inheritdoc
     */
    public static function tableName()
    {
        return 'news';
    }

    /**
     * @inheritdoc
     */
    public function rules()
    {
        return [
            [['category_id', 'sort', 'status'], 'integer'],
            [['title', 'slug', 'full_text'], 'required'],
            [['short_text', 'full_text'], 'string'],
            [['created_at', 'updated_at', 'updated_by', 'created_by'], 'safe'],
            [['title', 'slug'], 'string', 'max' => 255],
            ['image', 'image', 'extensions' => 'jpg, jpeg, gif, png', 'on' => ['insert', 'update']],
            [['lang'], 'string', 'max' => 6],
            [['category_id'], 'exist', 'skipOnError' => true, 'targetClass' => Category::className(), 'targetAttribute' => ['category_id' => 'id']],
        ];
    }

    /**
     * @return array
     */
    public function behaviors()
    {
        $module = Yii::$app->getModule('news');
        return [
            'sort' => [
                'class' => SortableGridBehavior::className(),
                'sortableAttribute' => 'sort',
            ],
            [
                'class' => TimestampBehavior::className(),
                'value' => new Expression('NOW()'),
            ],
            [
                'class' => UploadImageBehavior::className(),
                'attribute' => 'image',
                'scenarios' => ['insert', 'update'],
                'path' => $module->uploadPath,
            ],

        ];
    }

    /**
     * @inheritdoc
     */
    public function attributeLabels()
    {
        return [
            'id' => Yii::t('news/news', 'ID'),
            'category_id' => Yii::t('news/news', 'Category'),
            'title' => Yii::t('news/news', 'Title'),
            'slug' => Yii::t('news/news', 'Slug'),
            'short_text' => Yii::t('news/news', 'Short Text'),
            'full_text' => Yii::t('news/news', 'Full Text'),
            'image' => Yii::t('news/news', 'Image'),
            'created_at' => Yii::t('news/news', 'Created At'),
            'updated_at' => Yii::t('news/news', 'Updated At'),
            'created_by' => Yii::t('news/news', 'Created By'),
            'updated_by' => Yii::t('news/news', 'Updated By'),
            'sort' => Yii::t('news/news', 'Sort'),
            'status' => Yii::t('news/news', 'Status'),
            'lang' => Yii::t('news/news', 'Language'),
        ];
    }

    /**
     * @return \yii\db\ActiveQuery
     */
    public function getUpdatedBy()
    {
        return $this->hasOne(User::className(), ['id' => 'updated_by']);
    }

    /**
     * @return \yii\db\ActiveQuery
     */
    public function getCategory()
    {
        return $this->hasOne(Category::className(), ['id' => 'category_id']);
    }

    /**
     * @return array
     */
    public static function getStatusList()
    {
        return [
            self::STATUS_DISABLED => Yii::t('news/news', 'Disabled'),
            self::STATUS_ACTIVE => Yii::t('news/news', 'Active'),
        ];
    }

    /**
     * @return int|mixed
     */
    public function getStatusName()
    {
        $arr = $this::getStatusList();

        return array_key_exists($this->status, $arr) ? $arr[$this->status] : $this->status;
    }

    /**
     * @return array
     */
    public static function getLanguageList()
    {
        // TODO: Получить список языков приложения.
        return [
            'ru-RU' => Yii::t('news/news', 'Russian'),
            'en-US' => Yii::t('news/news', 'English'),
        ];
    }
}