Bug in the method GetShipmentTrackerAsync in nop 4.50.

How to show it.

Create the nop order with the shipping method. Create the shipment with a tracking code.
Save it.
Delete shipping method plugin from the nopcommerce.
Try to open this shipment, you will see error message
System.NullReferenceException: Object reference not set to an instance of an object.
   at Nop.Services.Shipping.ShipmentService.GetShipmentTrackerAsync(Shipment shipment)
   at Nop.Web.Areas.Admin.Factories.OrderModelFactory.PrepareShipmentModelAsync(ShipmentModel model, Shipment shipment, Order order, Boolean excludeProperties)
   at Nop.Web.Areas.Admin.Controllers.OrderController.ShipmentDetails(Int32 id)
   at

The reason of this error in the code
return await shippingRateComputationMethod?.GetShipmentTrackerAsync();
You need replace it with
                if (shippingRateComputationMethod != null)
                    return await shippingRateComputationMethod?.GetShipmentTrackerAsync();
                else
                    return null;

Please do it for the pickup too
This is the new correct code

        public virtual async Task<IShipmentTracker> GetShipmentTrackerAsync(Shipment shipment)
        {
            var order = await _orderRepository.GetByIdAsync(shipment.OrderId, cache => default);

            if (!order.PickupInStore)
            {
                var shippingRateComputationMethod = await _shippingPluginManager
                    .LoadPluginBySystemNameAsync(order.ShippingRateComputationMethodSystemName);
                if (shippingRateComputationMethod != null)
                    return await shippingRateComputationMethod?.GetShipmentTrackerAsync();
                else
                    return null;
            }

            var pickupPointProvider = await _pickupPluginManager
                .LoadPluginBySystemNameAsync(order.ShippingRateComputationMethodSystemName);
            if (pickupPointProvider != null)
                return await pickupPointProvider?.GetShipmentTrackerAsync();
            else
                return null;
        }

Thanks a lot for reporting. We'll fix it soon - https://github.com/nopSolutions/nopCommerce/issues/6334

done, please see this commit to more details