Pulling member name from WordPress URL

You should check if $current_member is empty, because get_user_by() would return false upon failure and a WP_User instance/object otherwise:

if ( empty( $current_member ) ) {
  return '';
}

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)