值不能为 null。 参数名: source

通过web api从生产用料清单下推采购补料单出错.

{"Result":{"ResponseStatus":{"ErrorCode":500,"IsSuccess":false,"Errors":[{"FieldName":null,"Message":"
值不能为 null。
参数名: source
Server stack trace: 
   在 System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   在 Kingdee.K3.MFG.PRD.App.BillConvertServicePlugIn.PpbomToFeedMtrConvert.OnAfterCreateLink(CreateLinkEventArgs e)
   在 Kingdee.BOS.Core.Metadata.ConvertElement.PlugIn.ConvertPlugInProxy.FireOnAfterCreateLink(CreateLinkEventArgs e)
   在 Kingdee.BOS.App.Core.Convertible.DefaultPolicy.FillLinkInfoAction.Do()
   在 Kingdee.BOS.Core.BusinessPolicyModel.BusinessPolicyEngine.Do(OperateOption context)
   在 Kingdee.BOS.App.Core.Convertible.ConvertEngine.OnCreating(PushArgs pushArgs, OperateOption option)
   在 Kingdee.BOS.App.Core.ConvertService.Push(Context ctx, PushArgs serviceArgs, OperateOption option, Boolean validPermission)
Exception rethrown at [0]: 
   在 System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   在 System.Runtime.Remoti