PHP Notice: Undefined index: post_types

Hello,
Contextual Related Posts v2.4.1

I can see an error with WP Debug, what’s the meaning?
PHP Notice: Undefined index: post_types in /xxxx/wp-content/plugins/contextual-related-posts/includes/modules/class-crp-widget.php on line 65

		// If post_types is empty or contains a query string then use parse_str else consider it comma-separated.
		if ( ! empty( $instance['post_types'] ) && false === strpos( $instance['post_types'], '=' ) ) {
			$post_types = explode( ',', $instance['post_types'] );
		} else {
			parse_str( $instance['post_types'], $post_types );	// Save post types in $post_types variable.
		}

The line 65 is the line with the comment // Save post types in $post_types variable.