Null reference exception occurs in 25R2 when my event handler supplies the second optional parameter

Question

I am getting examples of null reference exception error for some event handlers in 25R2 such as the following:

[NullReferenceException: Object reference not set to an instance of an object.]
   PX.Data.Generic`2.SearchAdapted(TGenericDelegate genericHandler, IEnumerable`1 classicHandlers) +258
   PX.Data.Generic`2.GetClassicHandler(TGenericDelegate handler, Boolean remove) +100
   PX.Data.RowInsertingEvents.AddAbstractHandler(Action`1 handler) +88
   PX.Objects.IN.GraphExtensions.LineSplittingExtension`4.SubscribeForSplitEvents() +198
   PX.Objects.IN.GraphExtensions.KitAssemblyEntryExt.INKitLineSplittingExtension.SubscribeForSplitEvents() +18
   PX.Objects.IN.GraphExtensions.LineSplittingExtension`4.Initialize() +309
   PX.Objects.IN.GraphExtensions.KitAssemblyEntryExt.INKitLineSplittingExtension.Initialize() +18
   PX.Data.PXGraph.CreateInstance(Type graphType, String prefix) +573
   PX.Web.UI.PXBaseDataSource.CreateDataGraphAsSingleton(Type type) +593
   PX.Web.UI.PXBaseDataSource.CreateDataGraph(Type type) +152
   PX.Web.UI.PXBaseDataSource.get_DataGraph() +414
   PX.Web.UI.PXPage.GetAttributesFound() +84
   PX.Web.UI.PXPage.EnableAttributes() +694
   PX.Web.UI.PXPage.OnInit(EventArgs e) +88
   System.Web.UI.Control.InitRecursive(Control namingContainer) +453
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1713

When reviewing the error, it suggests a problem with RowInserting for the split,

  PX.Data.RowInsertingEvents.AddAbstractHandler(Action`1 handler)

To overcome the problem I can comment out the second optional parameter (delegate) as shown below:


        protected void _(Events.RowInserting<INKitTranSplit> e) //, PXRowInserting del)
        {                
            //del?.Invoke(e.Cache, e.Args);
            INKitTranSplit row = e.Row;

but this is not ideal. The problem can occur with other events, all of them appear to involve the

PX.Objects.IN.GraphExtensions.LineSplittingExtension in the stack trace.

Has anyone else observed this issue? I wish to keep the delegate option.

jedmunds36 · Accepted Answer

The answer from Case Support I think is helpful:

For most DACs, the system already has a base event handler wired in. This means when you write your own handler, you can hook into the system’s logic using the delegate parameter (e.g., PXRowInserting del). In those cases, the delegate points to the default behavior, so you can call it before or after your custom code to preserve the original functionality.

With split DACs such as SOLineSplit, INTranSplit etc the situation is different. These aren’t primary records — they’re used for allocations (splitting quantities across lots, serials, warehouses, etc.), and the system creates and manages them behind the scenes. They are controlled by the LineSplittingExtension framework. Because of this, there aren’t any base event handlers like RowInserting or FieldDefaulting. If you attempt to add a delegate parameter (such as PXRowInserting del) in a handler for SOLineSplit or INTranSplit, the delegate will always be null.

For example, there is no FieldDefaulting handler on the TransferLineSplittingExtension, which extends INTranSplit through the LineSplittingExtension logic. Split events are not explicitly defined within the graph; instead, they are dynamically injected through the SubscribeForSplitEvents method. You can add your handlers, like it is done in TransferLineSplittingExtension.

jedmunds36 · Answer

Much like split-level, the PX.Objects.IN.GraphExtensions.LineSplittingExtension error can occur for SubscribeForLineEvents() for line-level events like below, again when the second param (eg delegate) is described:

        protected void _(Events.FieldVerifying<ARTran.qty> e, PXFieldVerifying del)
        {
            // call the base BLC event handler...
            del?.Invoke(e.Cache, e.Args);
            ARTran row = e.Row as ARTran;
            if (row == null) return;

but with a Field-level event, this can be avoided by describing the TTable in the first param:

        protected void _(Events.FieldVerifying<ARTran, ARTran.qty> e, PXFieldVerifying del)
        {
            // call the base BLC event handler...
            del?.Invoke(e.Cache, e.Args);
            ARTran row = e.Row as ARTran;
            if (row == null) return;

Null reference exception occurs in 25R2 when my event handler supplies the second optional parameter

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