private static function is_super_admin( $user_id ) {
            $is_super_admin = false;

            $user = self::_get_user_by_id( $user_id );

            if ( $user instanceof FS_User && ! empty( $user->email ) ) {
                self::require_pluggable_essentials();

                $wp_user = get_user_by( 'email', $user->email );

                if ( $wp_user instanceof WP_User ) {
                    $super_admins   = get_super_admins();
                    $is_super_admin = ( is_array( $super_admins ) && in_array( $wp_user->user_login, $super_admins ) );
                }
            }

            return $is_super_admin;
        }