DynamicFieldDB: Search in input field triggers an error when no value item is selected as search field

Given a field like

where no value item is selected as a search field, a search in the input field

triggers an error:

ERROR: OTOBO-CGI-80 Perl: 5.30.0 OS: linux Time: Fri Mar 11 08:06:18 2022

 Message: ERROR:  syntax error at end of input
LINE 1: ...ELECT login,first_name || ' ' || last_name FROM users WHERE 
                                                                       ^, SQL: 'SELECT login,first_name || ' ' || last_name FROM users WHERE '

 RemoteAddress: 172.17.0.1
 RequestURI: /otobo/index.pl?

 Traceback (263): 
   Module: Kernel::System::DynamicFieldDB::DatabaseSearchByConfig Line: 548
   Module: Kernel::Modules::AgentDynamicFieldDBSearch::Run Line: 311
   Module: Kernel::System::Web::InterfaceAgent::Content Line: 1239
   Module: Kernel::System::Web::InterfaceAgent::Response Line: 1321
   Module: Kernel::System::Web::App::call Line: 86
   Module: Plack::Component::__ANON__ Line: 50
   Module: Plack::App::URLMap::call Line: 71
   Module: Plack::Component::__ANON__ Line: 50
   Module: Plack::Sandbox::_2fopt_2fotobo_2fbin_2fpsgi_2dbin_2fotobo_2epsgi::__ANON__ Line: 200
   Module: Plack::Sandbox::_2fopt_2fotobo_2fbin_2fpsgi_2dbin_2fotobo_2epsgi::__ANON__ Line: 170
   Module: Plack::Sandbox::_2fopt_2fotobo_2fbin_2fpsgi_2dbin_2fotobo_2epsgi::__ANON__ Line: 156
   Module: Plack::Middleware::HTTPExceptions::try {...}  Line: 20

The WHERE clause is empty. I see three possible solutions:

• Do not save the dynamic field configuration unless (at least) one value item is selected as search field
• Use the first value item as the default search field
• Use the identifier as the default search field