// Type: long?, selector function is called public static int Test4g() { Data_Nlong[] source = new Data_Nlong[]{ new Data_Nlong{name="Tim", num=null}, new Data_Nlong{name="John", num=-105L}, new Data_Nlong{name="Bob", num=Int64.MaxValue} }; long? expected = Int64.MaxValue; var actual = source.Max((e) => e.num); return ((expected == actual) ? 0 : 1); }