业务规则 - 指定的演员表无效

Question

我已经搜索了这个问题的答案，但似乎无法找到适合我的情况，或者我还没有掌握它。我正在为我公司的商业软件制定业务规则，并且收到“指定的演员表无效”错误。我知道它与char变量和/或null有关，我只是无法弄清楚如何修复它或为什么我得到错误（它可能很简单）。

以下是规则的代码。它应该将unit_price与price1（表中的两个字段）进行比较，如果price1更高，则将unit_price替换为price1，并且对表中的每一行执行此操作。

我有代码工作，直到我尝试添加Class4。 Class4指定具有锁定价格的项目。这用于防止价格锁定的商品价格变动。 Class4是表中的char [8]字段，有两个值，LOCKED和null。这是我的问题开始的地方。

为了合法目的，我删除了对该计划的引用。

如果我的代码混乱或完全无效或不正确，请原谅我。我对c＃很新，并且大部分都在猜测。

    public class PriceCheck : program.Extensions.BusinessRule.Rule
    {
        decimal Unit = 0m;
        decimal Price1 = 0m;
        String Class4;
        DataTable datatable1;
        Boolean bDebugMode = true;
        int TriggerRow;

        public override RuleResult Execute()
        {
            RuleResult result = new RuleResult();
            result.Success = true;

            if (bDebugMode) MessageBox.Show("Starting PriceCheck"); //MessageBox for debugging purposes, shows that PriceCheck has begun

            try
            {
                if (this.Session.MultiRow)
                {
                    datatable1 = this.Data.Set.Tables["Table"]; //Set table information will be pulled from and sent to
                    TriggerRow = this.Data.TriggerRow;

                    foreach (DataRow row in (InternalDataCollectionBase)datatable1.Rows) //Begin loop for all rows in datatable1
                    {
                        Unit = DataRowExtensions.Field<Decimal>(row, "unit_price"); //Retrieve Unit Price from current row
                        Price1 = DataRowExtensions.Field<Decimal>(row, "inv_mast_price1"); //Retrieve Price1 from current row
                        Class4 = Convert.ToString(DataRowExtensions.Field<Char?>(row, "class_id4")); //Retrives Class4 from current row
                        if (bDebugMode) MessageBox.Show("Unit Price " + Unit + "\n" + "Price 1 " + Price1 + "\n" + "Class 4" + Class4, "Debug", MessageBoxButtons.OKCancel, MessageBoxIcon.Information); //MessageBox for debugging, shows values in Unit, List, and Class4

                        if (Class4 == "LOCKED")
                        {
                            if (bDebugMode) MessageBox.Show("Class 4 Locked" + "\n" + "Unit Price will remain the same!" + "\n" + "Unit Price " + Unit, "Class 4 Locked", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                        }
                        else
                        {
                            if (Unit > 0) //if unit is null(0), the rule will fail, this is here to prevent that...might change to item Id, depending on if any items have 0 Unit Price and Price 1
                            {
                                if (bDebugMode) MessageBox.Show("Unit > 0", "Unit Check", MessageBoxButtons.OK, MessageBoxIcon.Information); //MessageBox for debugging, shows that this if statement has been reached

                                if (Unit < Price1) //beginning of calculations
                                {
                                    if (bDebugMode) MessageBox.Show("Price 1 " + Price1, "Debug", MessageBoxButtons.OKCancel, MessageBoxIcon.Exclamation); //Shows Price1 before putting it into the unit_price field
                                    DataRowExtensions.SetField<Decimal>(row, "unit_price", Price1); //assigns Price1 to the unit_price field
                                }
                                else
                                {
                                    if (bDebugMode) MessageBox.Show("Unit Price" + Unit, "Debug", MessageBoxButtons.OKCancel, MessageBoxIcon.Exclamation); //Shows Unit Price before assigning it to the unit_price field
                                    DataRowExtensions.SetField<string>(row, "unit_price", Convert.ToString(Unit)); //assigns Unit to the unit_price field
                                }
                            }

                        }
                    }
                }
            }
            catch (Exception ex)
            {
                result.Success = false;
                result.Message = ex.Message;
            }
            if (bDebugMode) MessageBox.Show("Ending Price Check"); //MessageBox for debugging, shows the end of the calculations before result is returned
            return result;
        }
        public override string GetDescription()
        {
            return "Checks prices to keep Unit Price above minimum.";
        }
        public override string GetName()
        {
            return "Price Check";
        }
    }
 }