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Hi Andrew

I can do that on https://swiftdemo.dynamicweb-cms.com/ - you can try with DemoUser/DemoUser123 and check it out.'

So you might have a cart related setting or something custom.

This is the code that seems to fail:

Seems like you have orderlines with no product ids or something like that.

It could be nice to see the EcomOrderlines for the cart that is causing the issues.

We can of course skip this code if there are orderlines with missing product ids or what is causing this.

Thanks Nicolai.  I also suspected that as this piece of code changed from between version 9.15.3 and 9.5.13 when I compared the dlls.
However I was pointed in the right direction to resolve the issue.
 

I think what I missed in the stack trace was the Notification Manager - I think this would indicate that the CreateCartViewModel was being called from a notification subscribe (but maybe I'm wrong) 

[ArgumentNullException: Value cannot be null.
Parameter name: key]
   System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument) +52
   System.Collections.Generic.Dictionary`2.FindEntry(TKey key) +14578763
   System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value) +21
   Dynamicweb.Ecommerce.ProductCatalog.ViewModelFactory.CreateCartViewModel(Order cart, Nullable`1 areaId) +2387
   Dynamicweb.Ecommerce.Frontend.EcomPageOnOutputSubscriber.CreateInstance(Order cart, Nullable`1 areaId) +102
   Dynamicweb.Ecommerce.Frontend.EcomPageOnOutputSubscriber.OnNotify(String notification, NotificationArgs args) +375
   Dynamicweb.Extensibility.Notifications.NotificationManager.Notify(String notification, NotificationArgs eventArgs) +875
   Dynamicweb.Frontend.PageView.Output() +1513
   Dynamicweb.AspNet.DynamicwebHttpHandler.ProcessRequest(HttpContext context) +71
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +542
   System.Web.<>c__DisplayClass285_0.<ExecuteStepImpl>b__0() +38
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +11857797
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +93

Anyway, the issue was I had a custom notification subscriber that I created for future use -  in order to clear custom order fields when a user does a re-order, I need to clear payment information as this is duplicated with the order).
This was passing a NULL Cart object to CreateCartViewModel.  Although this didn't seem to give an issue in 9.9.5 but does in 9.15.3.

[Subscribe(Dynamicweb.Ecommerce.Notifications.Ecommerce.Cart.Created)]

Good find. And one of the wonders of changing any code over the lifespan of a product :-)

I'm still investigating this - I thought it was resolved, but it seems to only occur if there are discount lines on the order - and it may be even be occuring due to LS OMNI live integration with regards to discounts as it clears and uses discount calculated by LS.

If you create an order on the front end and just use that session then its fine.  But if I log out and then log back in I get the NULL parameter problem.

If there is no discount then the problem doesn't occur.

Difficult to debug

Could indicate a wrong orderlinetype of the discounts coming from omni - or a missing orderlineid. That has to be set manually.

Hi Nicolai,

It was never an issue when we were on 9.9.2 because CreateCartViewModel didn't exist in Ecommerce.dll at that stage as far as I could tell.
The problem also only occurs when you log out and log back in.
So if you add item to cart and omni calculates discount line and adds to order then everything is fine - the discount appears in the OrderLine table (to note the product number is NULL anlong with variant id = NULL, but everythign works fine).

The issue only occurs if you log out and back in or create another session via an incognito window.

This is the XML from live integration when it gets it back from omni - notice that for discount lines there is no itemid or product id.
Could this maybe where the product code in CreateCartViewModel is failing?
 <OrderDiscountLines>
    <OrderDiscountLine>
      <ExtensionData />
      <Id />
      <Description>10% Off Treat</Description>
      <DiscountAmount>164.00</DiscountAmount>
      <DiscountPercent>10.00</DiscountPercent>
      <DiscountType>TotalDiscount</DiscountType>
      <LineNumber>1</LineNumber>
      <No>1</No>
      <OfferNumber>5000PDISC0000387</OfferNumber>
      <OrderId />
      <PeriodicDiscGroup />
      <PeriodicDiscType>Unknown</PeriodicDiscType>
    </OrderDiscountLine>
  </OrderDiscountLines>
  <OrderLines>
    <OrderLine>
      <ExtensionData />
      <Id />
      <Amount>1476.00</Amount>
      <DiscountAmount>164.00</DiscountAmount>
      <DiscountPercent>10.00</DiscountPercent>
      <ItemDescription>Dipbrow Pomade</ItemDescription>
      <ItemId>113163</ItemId>
      <ItemImageId />
      <LineNumber>1</LineNumber>
      <LineType>Item</LineType>
      <NetAmount>1283.48</NetAmount>
      <NetPrice>356.52</NetPrice>
      <OrderId />
      <Price>410.00</Price>
      <Quantity>4.00</Quantity>
      <QuantityOutstanding>0</QuantityOutstanding>
      <QuantityToInvoice>4.00</QuantityToInvoice>
      <QuantityToShip>0</QuantityToShip>
      <TaxAmount>192.52</TaxAmount>
      <UomId />
      <VariantDescription>AUBURN</VariantDescription>
      <VariantId>AUBURN</VariantId>
    </OrderLine>

This is how the discount initially appears on teh OrderLines table - and you can checkout and add more items, etc.
However as soon as I log out and back in, I get an error and the Discount line has been removed fromteh table by live integration - so I assume the process is that live integration removes all discount lines and re-adds them.

Hi Andrew

There is a setting to tell if carts should be recalculated on login - not sure it will impact this though. See below.

From the response I can see that the orderlines have no ID - that is what is causing this I guess. I made a pull request to make it less volatile to that - code looks like this:

Yeah, that setting didn't make a difference.

How do I get hold of the change, Is this in a repository somewhere and do I need access?

In order to solve this from the live integration side, I changed the discount line to force it to have an ID when adding to the Order object.
As there is one discount per line I just made it the related productLine ID and concatenated _1 onto the end: discountOrderLine.Id = productOrderLine.Id + "_1";

It resolves the issue, but not sure its the most elegant way.