ServiceStack Ormlite SqlExpressionVisitor null check in Where extension -

i write method querying table 1 method null cheking parameters using sqlexpressionvisitor of ormlite here method :

public static list<userchatsdto> getuserchats(int startrow, int rowcount, datetime? startdate, datetime? enddate, string operatorname, short? rating, string visitorname)         {             using (idbconnection db = dbfactory.opendbconnection())             {                 sqlexpressionvisitor<userchatsdto> ev = ormliteconfig.dialectprovider.expressionvisitor<userchatsdto>();                 ev.where(q =>                      (startdate.hasvalue && q.dated >= startdate) &&                      (enddate.hasvalue && q.dated <= enddate) &&                     (!string.isnullorempty(operatorname) && q.takenbyuser.contains(operatorname)) &&                     (rating.hasvalue && q.rating == (short)rating) &&                     (!string.isnullorempty(visitorname) && q.visitorname.contains(visitorname)));                 //ev.orderby();                 ev.limit(startrow, rowcount);                 return db.select<userchatsdto>(ev);             }         } 

but object reference not set instance of object. nullreferenceexception thrown when call ev.where part.

is there bug here or missing ? thank you.

you can build expressionvisitor inside select method so:

var chats = db.select<userchatsdto>(q => q     .where(x => startdate.hasvalue && x.date >= startdate)     .where(x => enddate.hasvalue && x.date <= enddate)     .where(x => string.isnullorempty(operatorname) || x.takebyuser.contains(operatorname))     .where(x => rating.hasvalue && x.rating == (short)rating)     .where(x => string.isnullorempty(visitorname) || x.visitorname.contains(visitorname)     .limit(startrow, rowcount));