请高手指导，单据转换时，对字段长度（或字段标识长度）是否有限制？
单据转换时提示报错“Object reference not set to an instance of an object.”
详细报错信息：
发生时间：18:01:50
错误来源： mscorlib
错误信息：Object reference not set to an instance of an object.
===================================================
调用堆栈：
Server stack trace:
at Kingdee.BOS.App.Core.Convertible.MappingHelper.MappingBaseDataField.MappingValue()
at Kingdee.BOS.App.Core.Convertible.DefaultPolicy.FieldMappingAction.MappingValue(ExtendedDataEntity extEntity, IMappingField mapping, Field targetField, Object mapValue, Object sourceOrgBDId)
at Kingdee.BOS.App.Core.Convertible.DefaultPolicy.FieldMappingAction.Do()
at Kingdee.BOS.Core.BusinessPolicyModel.BusinessPolicyEngine.Do(OperateOption context)
at Kingdee.BOS.App.Core.Convertible.ConvertEngine.OnCreating(PushArgs pushArgs, OperateOption option)
at Kingdee.BOS.App.Core.ConvertService.Push(Context ctx, PushArgs serviceArgs, OperateOption option, Boolean validPermission)
Exception rethrown at [0]:
at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)
at Kingdee.BOS.Contracts.IConvertService.Push(Context ctx, PushArgs serviceArgs, OperateOption option, Boolean validPermission)
at Kingdee.BOS.ServiceHelper.ConvertServiceHelper.Push(Context ctx, PushArgs serviceArgs, OperateOption option)
at Kingdee.BOS.Business.Bill.Operation.SpecPush.Push()
at Kingdee.BOS.Business.Bill.Operation.SpecPush.ExecuteOperation()
at Kingdee.BOS.Core.DynamicForm.AbstractDynamicFormOperation.Operation(CallBackWfAfterOperation callbackwf, IOperationResult result)
at Kingdee.BOS.Core.DynamicForm.AbstractDynamicFormOperation.Execute(InvokeFormOperation4WfParam param, CallBackWfAfterOperation callbackwf)
at Kingdee.BOS.Web.DynamicForm.OperationCaller.InvokeFormOperation(String operationNumber)
at Kingdee.BOS.Business.DynamicForm.BusinessService.ExcuteOperation.DoAction(FormBusinessServiceArgs e)
at Kingdee.BOS.Core.DynamicForm.FormBusinessServiceUtil.InvokeServices(IDynamicFormView view, Object source, IEnumerable`1 services, Int32 actionType, String activeEntity, DynamicObject activeRow, Int32 rowIndex)
at Kingdee.BOS.Web.DynamicForm.BusinessServiceCaller.InvokeFormBusiness(IDynamicFormView view, Object source, List`1 formBusinessServices, Int32 actionType, String entityKey, Int32 row)
at Kingdee.BOS.Web.DynamicForm.DynamicWebFormView.BarItemClick(String parentKey, String barItemKey, BarDataManager bar, Int32 bartype)
at Kingdee.BOS.Web.DynamicForm.DynamicWebFormView.MainBarItemClick(String barItemKey)
at Kingdee.BOS.Web.DynamicForm.DynamicWebFormController.MainBarItemClick(String itemKey, JSONArray postDatas)
错误数据： System.Collections.ListDictionaryInternal
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