public function get_post_types( $source_id = null ) {
		$post_types = WPRSS_FTP_Settings::get_post_types();
		if ( is_null($source_id) ) {
			return $post_types;
		}

		$assigned_type = self::get_instance()->get_meta( $source_id, 'post_type' );
		if( $assigned_type && !isset($post_types[$assigned_type]) ) {
			$post_types[$assigned_type] = sprintf( '%1$s (%2$s)', $assigned_type, __( 'Not Registered', WPRSS_TEXT_DOMAIN ) );
		}

		return $post_types;
	}