[Koha] searching error after upgrading from 3.14.05 to 3.18.05.1

Hi List, Our Koha 3.14.05 tarball installed on linux Ubuntu We have some problem, after upgrading to 3.18.05.1 When searching the catalogue we get Error: Can't call method "raw" on an undefined value at /usr/share/koha/lib/C4/Search.pm line 800. Please help as soon as possible. Thanks, Araik