How can I check for a null value while loading a list with a reader??

Question

The description field is null in my database and whenever the following code tries to load a list it throws an exception, I have searched all over and tried several things I thought would work.  I am new to C# coming from VB so forgive my ignorance.  Thank you for your time!

public static List<Subcategories> GetSubcategories(int SubgroupID)

{

using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["XXX"].ConnectionString))

{

using (SqlCommand command = new SqlCommand("GetSubcategories", connection))

{

command.CommandType = CommandType.StoredProcedure;

command.Parameters.Add(new SqlParameter("@SubgroupID", SubgroupID));

connection.Open();

List<Subcategories> list = new List<Subcategories>();

using (SqlDataReader reader = command.ExecuteReader())

{

while (reader.Read())

{

Subcategories temp = new Subcategories(

(int)reader["SubCategoryId"],

(int)reader["SubgroupID"],

(string)reader["Title"],

(string)reader["Manager"],

(string)reader["Description"]);   <----- THIS LINE IS WHERE THE FAILUER OCCURS!

list.Add(temp);

}

}

return list;

}

}

}