c# - Nhibernate Query Over exception on join with invalid value -

-- tbl_region-- id  displayname description isusinglinenumbers    waitperiod     fk_stateid 1   ups            upstate         0                   10          1 2   dwn            downstate       1                   20          1 3   ok             oklahoma        1                   15          2  -- clientidentifier--  id  clientid    fk_regionid 1   prci1             1 2   prci2             2 3   prci3             3  var clientidentifier =  session.queryover<clientidentifier>()     .where(x => x.clientid == clientid).joinqueryover(x=>x.region)     .singleordefault(); 

this query throwing exception when clientid not valid. how can avoid ?

if need deal nullables properties in queries can use this:

var query = session.queryover<clientidentifier>()  if (clientid == null)     query = query.whererestrictionon(x => x.clientid).isnull; else     query = query.where(x => x.clientid == clientid);  var clientidentifier =  query.joinqueryover(x => x.region)     .singleordefault();