DataReader索引超出数组的界限

我有以下方法从表中提取信息；

public Customer GetCustomerDetails(int customerID)
    {
        Customer currentCustomer = null;
        try
        {
            using (cxn = new SqlConnection(this.ConnectionString))
            {
                using (cmd = new SqlCommand("spGetCustomerInformation", cxn))
                {
                    cmd.CommandType = CommandType.StoredProcedure;
                    cmd.Parameters.Add("@CustomerID", SqlDbType.Int).Value = customerID;
                    cxn.Open();
                    SqlDataReader dataReader = cmd.ExecuteReader();
                    currentCustomer = new Customer();
                    currentCustomer.CustomerID = customerID;
                    while (dataReader.Read())
                    {
                        currentCustomer.FirstName = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.firstName)).ToString();
                        currentCustomer.Surname = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.surname)).ToString();
                        currentCustomer.Email = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.email)).ToString();
                        currentCustomer.Phone = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.phone)).ToString();
                        currentCustomer.AddressLine1 = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.addressLine1)).ToString();
                        currentCustomer.AddressLine2 = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.addressLine2)).ToString();
                        currentCustomer.City = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.city)).ToString();
                        currentCustomer.County = dataReader.GetValue(Convert.ToInt32(CustomerTableColumns.county)).ToString();
                    }
                    dataReader.Close();
                    cxn.Close();
                }
            }
        }
        catch (SqlException)
        {
            throw;
        }
        return currentCustomer;
    }

然而，我一直收到错误"System.Data.dll 中发生了类型为"System.IndexOutOfRangeException"的未处理异常

附加信息：索引超出了数组的界限。"在while循环的最后一行。

我的SQL查询如下：

ALTER PROC [dbo].[spGetCustomerInformation]
@CustomerID INTEGER
AS 
BEGIN
SET NOCOUNT ON
SELECT
a.Firstname,
a.Surname,
a.Email,
a.Phone,
a.AddressLine1,
a.AddressLine2,
a.City,
County
FROM 
tblCustomers a
WHERE
a.CustomerID = @CustomerID
END