.net AddWithValue 参数为 NULL 时的异常

下面是为SQL查询指定参数的代码.当我使用Code 1时，我得到以下异常；但当我使用Code 2时效果很好.在Code 2中，我们判断null，因此有if..else块.

例外情况:

The parameterized query '(@application_ex_id nvarchar(4000))SELECT E.application_ex_id A' expects the parameter '@application_ex_id', which was not supplied.个

Code 1:

command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);

Code 2:

if (logSearch.LogID != null)
{
         command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
}
else
{
        command.Parameters.AddWithValue("@application_ex_id", DBNull.Value );
}

QUESTION

1. 你能解释一下为什么不能从logSearch中获取NULL吗.代码1中的LogID值(但能够接受DBNull)？

2. 有更好的代码来处理这个问题吗？

Reference:

1. Assign null to a SqlParameter
2. Datatype returned varies based on data in table个
3. Conversion error from database smallint into C# nullable int个
4. What is the point of DBNull?

密码

    public Collection<Log> GetLogs(LogSearch logSearch)
    {
        Collection<Log> logs = new Collection<Log>();

        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            string commandText = @"SELECT  *
                FROM Application_Ex E 
                WHERE  (E.application_ex_id = @application_ex_id OR @application_ex_id IS NULL)";

            using (SqlCommand command = new SqlCommand(commandText, connection))
            {
                command.CommandType = System.Data.CommandType.Text;

                //Parameter value setting
                //command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
                if (logSearch.LogID != null)
                {
                    command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
                }
                else
                {
                    command.Parameters.AddWithValue("@application_ex_id", DBNull.Value );
                }

                using (SqlDataReader reader = command.ExecuteReader())
                {
                    if (reader.HasRows)
                    {
                        Collection<Object> entityList = new Collection<Object>();
                        entityList.Add(new Log());

                        ArrayList records = EntityDataMappingHelper.SelectRecords(entityList, reader);

                        for (int i = 0; i < records.Count; i++)
                        {
                            Log log = new Log();
                            Dictionary<string, object> currentRecord = (Dictionary<string, object>)records[i];
                            EntityDataMappingHelper.FillEntityFromRecord(log, currentRecord);
                            logs.Add(log);
                        }
                    }

                    //reader.Close();
                }
            }
        }

        return logs;
    }