ExecuteScalar抛出NullReferenceException

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

    using (SqlCommand command = new SqlCommand(sqlQuery, connection))
    {
        object result = command.ExecuteScalar();

        if (result != null)
        {
            // 处理查询结果
        }
        else
        {
            // 处理空结果
        }
    }
}