command.Parameters.AddWithValue("@revcode",null);
 if (revcode != null)
 command.Parameters["@revcode"].Value = revcode.ToString();

public int UpdateTask(int id, IOrderedDictionary content)
        {
            int i = -1;
            try
            {
                using (SqlConnection connection = new SqlConnection(connectionString))
                {
                    connection.Open();
                    SqlCommand command = connection.CreateCommand();
                    StringBuilder sb = new StringBuilder("update tasks set ");
                    int count = content.Count;
                    string[] keys = new string[count];
                    object[] values = new object[content.Count];
                    content.Keys.CopyTo(keys, 0);
                    content.Values.CopyTo(values, 0);
                    for(int c=0;c<count;c++)
                    {
                        sb.Append(string.Format("\n,{0}=@{0}",keys[c]));
                        command.Parameters.AddWithValue("@"+keys[c],values[c]==null?DBNull.Value:values[c]);
                    }
                    sb.Append("\n where id=@id");
                    sb.Remove(17, 2);
                    command.CommandText = sb.ToString();
                    command.Parameters.AddWithValue("@id", id);
                    command.ExecuteNonQuery();
                    i = 1;