Не могу отобразить миниатюру, что не так?

<?php
private $meta_settings = array(
		'title' => 'Рейтинг:', 
		'slug' => 'rating',
		'input_type' => 'input',
		'post_type' => 'portfolio',
		'empty_message' => '0' 
	);
		private $cb_meta_settings = array(
		'title' => 'Миниатюра', 
		'slug' => 'thumbnail',
		'input_type' => 'input',
		'post_type' => 'portfolio',
		'empty_message' => 'Нет миниатюры'
	);

	/**
	 * Initial setup. Called by get_instance.
	 */
	protected function init() {

		add_filter( 'manage_'.$this->meta_settings['post_type'].'_posts_columns', array( $this, 'edit_meta_columns' ), 1 );
		add_action( 'manage_'.$this->meta_settings['post_type'].'_posts_custom_column', array( $this, 'manage_meta_columns' ), 10, 2 );
		add_filter( 'manage_'.$this->cb_meta_settings['post_type'].'_posts_columns', array( $this, 'cb_edit_meta_columns' ), 1 );
		add_action( 'manage_'.$this->cb_meta_settings['post_type'].'_posts_custom_column', array( $this, 'cb_manage_meta_columns' ), 10, 2 );

	}

	/**
	 * Add column for Meta on CPT
	 */
	function edit_meta_columns( $columns ) {

		$columns[$this->meta_settings['slug']] = $this->meta_settings['title'];

		return $columns;
	}
	function cb_edit_meta_columns( $columns ) {

		$columns[$this->cb_meta_settings['slug']] = $this->cb_meta_settings['title'];

		return $columns;
	}

	/**
	 * Populate column
	 */
	function manage_meta_columns( $column, $post_id ) {
		global $post;

		switch( $column ) {

			/* If displaying our custom meta column. */
			case $this->meta_settings['slug'] :

				/* Get the post meta. */
				$custom_meta = get_post_meta( $post_id, $this->meta_settings['slug'], true );

				/* If no custom meta is found, output a default message. */
				if ( empty( $custom_meta ) )
					echo $this->meta_settings['empty_message'];
				else
					echo '<div class="storm-meta-input" id="storm-meta-input-' . $post_id . '">' . get_post_meta( $post_id, $this->meta_settings['slug'], true ) . '</div>';
				break;

			default :
				break;
		}
	}

	function cb_manage_meta_columns( $column, $post_id ) {
		global $post;

		switch( $column ) {

			case $this->cb_meta_settings['slug'] :

				$cb_custom_meta = get_post_meta( $post_id, $this->cb_meta_settings['slug'], true );

				if ( empty( $cb_custom_meta ) )
					echo $this->cb_meta_settings['empty_message'];
				else
					echo '<div class="storm-meta-input" id="storm-meta-input-' . $post_id . '">' . get_post_meta( $post_id, $this->cb_meta_settings['slug'], true ) . '</div>';
				break;

			default :
				break;
		}
	}