```
 int id = 1;
 string[] employerNos = null;
 var query = from y in mydb.myTable
             where y.ID == id
             && (employerNos == null ? true : employerNos.Contains(y.EmpNo))                             
             select y;
 var result = query.ToList();

```

The string array is null so I think the statement should be true. I don't know why it throws System.NotSupportedException.