SqlCeCommand nullable values

My code:

SqlCeConnection sql = new SqlCeConnection(@"Data Source=C:\DB.sdf");
sql.Open();
cmd = new SqlCeCommand("INSERT INTO xxx(aaa) VALUES(@aaa)", sql);
String param = null;  //doesn't work
//String param = "blah" //works
cmd.Parameters.AddWithValue("@aaa", param);
cmd.ExecuteNonQuery(); //(1)
sql.Close();

(1) throws an exception when param is null. Database allows value in collumn aaa to be null. How can I insert null into table xxx ?

Exception:

Parameterized query 'INSERT INTO xxx(aaa) VALUES(@aaa)' expects a parameter value which w开发者_JAVA技巧as not supplied.

---

Try using DBNull.Value instead:

var param = DBNull.Value;

---

Use

var param = DBNull.Value;

null isn't the same thing as DBNull