c# - List.contains throwing null exception? -

i have join query like

 public actionresult import(int[] uservalue, int[] provalue, datetime? startdate, datetime? enddate)     {         list<int> actallid = db.activitys.select(x=>x.id).tolist();         list<int> actchild = fileoperation.childactivity(actallid);          datetime start_date = convert.todatetime(startdate);         datetime end_date = convert.todatetime(enddate);         ienumerable<viewmodelactivitysearch> search = r in db.reports         join in db.activitys on r.id equals a.report_id          join u in db.users on r.users_id equals u.id         join p in db.projects on a.projects_id equals p.id         join act in db.activitytypes on a.activity_type_id equals act.id         (         (r.start_date == startdate || r.end_date == enddate || uservalue.contains((int)r.users_id) || provalue.contains((int)a.projects_id))         &&         //status submitted=2, approved=3,exclude child activities         (!actchild.contains((int)a.id))           &&          (r.status == 2 || r.status == 3)          )         select new viewmodelactivitysearch         {          id = a.id,          activity_text = a.activity_text,          deliverable = a.deliverable,          employee = string.concat(u.firstname, " ", u.lastname),          start_date = r.start_date,          end_date = r.end_date,          activity_date = a.activity_date,          project = p.name,          category = act.activity_type          };         bindprojectanduser();         return view(search.tolist());     } 

i have search page user can enter start date,enddate,choose users , choose projects. made join query fetch data according variables. problem when user doesnot choose user or project code

uservalue.contains((int)r.users_id) || provalue.contains((int)a.projects_id)) 

gives error

 unable create null constant value of type 'system.int32[]'. entity types, enumeration types or primitive types supported in context. 

what else can use instead of contains error not arises. thanks

check null in values try cast explicitly int (like r.users_id) ternary operator before using contains:

where (r.start_date == startdate || r.end_date == enddate ||  r.users_id != null? uservalue.contains((int)r.users_id) : false ||  a.projects_id != null ?provalue.contains((int)a.projects_id) : false) 

method contains() method check if there's value in list of values of same type , it's fine use here.