Overriding an Action but the Override Action Delegate is null

I am trying to override an action on the Production Orders screen.  I am following the instructions that @Naveen Boga provided here:

However, when I get to the invoke method the “BaseMethod” is null and throws an error.

The override fires when you click the button, but the Delegate is null.

[PXOverride]
public delegate IEnumerable LinkSalesOrderDelegate(PXAdapter adapter);
[PXButton]
[PXUIField]
public IEnumerable LinkSalesOrder(PXAdapter adapter, LinkSalesOrderDelegate BaseMethod)
{
	AMProdItem curr = Base.ProdItemSelected.Current;
	if (curr == null) return adapter.Get();

	//if parent is filled, it is NOT the original, so don't unlink the prod order from the SO
	if (curr.ParentOrdID != null)
	{
		curr.OrdNbr = null;
		curr.OrdLineRef = null;
		curr.OrdTypeRef = null;
		curr.CustomerID = null;

		AMProdItemExt ext = curr.GetExtension<AMProdItemExt>();
		if (ext != null)
		{
			ext.UsrItemPrice = null;
			ext.UsrOrderQty = null;
		}

		Base.ProdItemSelected.UpdateCurrent();
		Base.Actions.PressSave();

		return adapter.Get();
	}
	else
	{
		AMProdItemExt ext = curr.GetExtension<AMProdItemExt>();
		if (ext != null)
		{
			ext.UsrItemPrice = null;
			ext.UsrOrderQty = null;
		}
		Base.ProdItemSelected.UpdateCurrent();

		return BaseMethod.Invoke(adapter);
	}
}

Any ideas why?

The goal: if you unlink a SO from a Production Order and the current order is not the “Parent” order, I don’t want to remove the Parent Production order from the SOLine.