调用WebAPI报错

报错：
未处理Kingdee.BOS.WebApi.Client.ServiceException
HResult=-2147467259
Message=ORA-01400: cannot insert NULL into ("CRMDATE"."NBG_T_CRUDEDATA"."FENTRYID")
Source=Kingdee.BOS.ServiceFacade.KDServiceFx
ErrorCode=-2147467259
WebEventCode=0
ClassName=Kingdee.BOS.ServiceFacade.ServiceException
ExceptionMethod=8
Execute
Kingdee.BOS.ServiceFacade.KDServiceFx, Version=5.1.250.5, Culture=neutral, PublicKeyToken=null
Kingdee.BOS.ServiceFacade.KDServiceFx.ServiceExecutor
System.String Execute(Kingdee.BOS.ServiceFacade.KDServiceFx.KDServiceContext, Kingdee.BOS.ServiceFacade.KDServiceFx.ServiceType, System.String[], Kingdee.BOS.ServiceFacade.SerializerProxy, Kingdee.BOS.ServiceFacade.KDServiceFx.ServiceType)
Handled=false
StackTrace:
在 Kingdee.BOS.ServiceFacade.KDServiceFx.ServiceExecutor.Execute(KDServiceContext context, ServiceType svcType, String[] paraValues, SerializerProxy serializeProxy, ServiceType beginMethod)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.ExecuteServiceModule.OnProcess(KDServiceContext context)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.ModulePipeline.ExcuteRequest(KDServiceContext context)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.RequestExcuteRuntime.BeginRquest(RequestExtractor requestExtractor, WebContext webCtx)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.RequestExcuteRuntime.StartRequest(RequestExtractor requestExtractor, WebContext context)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.KDSVCHandler.ExecuteRequest(WebContext ctx, RequestExtractor requestExtractor)
在 Kingdee.BOS.ServiceFacade.KDServiceFx.KDSVCHandler.ProcessRequestInternal(WebContext webCtx, RequestExtractor requestExtractor)
InnerException:

Json字符串
{
"Creator": "String",
"NeedUpDateFields": [
"String"
],
"Model": {
"FID": 0,
"FBillNo": "String",
"FDocumentStatus": "String",
"F_NBG_CargoOweer": "宁波港",
"F_NBG_Year": 2015,
"F_NBG_Month": 1
}
}

老师，这Json字符串写的有问题，还是怎么回事？