How to validate null Value?

Question

My Source code is
SQl = "select ActiveRate from co_batchwiserate where batchid ='" + CrsList.GetBatchID.ToString().Trim() + "'  and delstate <> 1";  SqlCommand cmd = new SqlCommand(SQl, SCon.GetConn()); strValue = (string)cmd.ExecuteScalar();  validate Stvalue is null or empty means  validate this strvalue if (strValue == null)         {             LblErr.Text = "Invalid Course Amount";             return;         }

Vulpes · Answer

I think you'll get back DBNull.Value rather than null if there's no match for that query but you can check for both or an empty string as follows:
object obj = cmd.ExecuteScalar();
if (Convert.IsDBNull(obj) || obj == null || obj.ToString() == "") {     LblErr.Text = "Invalid Course Amount";     return; }  else {     strValue = obj.ToString();     // do something with strValue }