c# - Fetch first element from a collection -

i'm trying first element collection , i'm getting error :

a fetch request must simple member access expression; '[100002]' subqueryexpression instead. parameter name: relatedobjectselector.

my query :

var allconferences = session.query<conferencedao>()                 .fetch(i => i.incident)                 .thenfetch(s => s.sheets.firstordefault()) //here need first sheet                 .thenfetch(v => v.victims)                 .projectto<telephonyconference>(); 

i've tried :

var subq = queryover.of<incidentdao>().selectlist(x => x.selectmin(y => y.sheets));   var allconferences = session.queryover<conferencedao>()             .fetch(i => i.incident).eager             .withsubquery.whereproperty(x => x.incidentid).in(subq)             .list()             .asqueryable()             .fetch(b=>b.victims)             .fetch(a => a.agency)             .projectto<telephonyconference>();          return allconferences; 

but i'm getting error :

"there no method 'fetch' on type 'nhibernate.linq.eagerfetchingextensionmethods' matches specified arguments"

any idea how can solve this? thanks