// If we have don't have a new value but do have an old one, delete it.
if ( ! $new_value && $old_value )
delete_post_meta( $this->manager->post_id, $this->name );
// If the new value doesn't match the old value, set it.
else if ( $new_value !== $old_value )
update_post_meta( $this->manager->post_id, $this->name, $new_value );
Could you please follow WordPress PHP Coding Standards?
I'm partucularly asking about braces: https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#brace-style
Example:
Adding
{}
will greatly improve readability.