Setting property to null does not always erase it

[tiagoshibata]

• OS and version used: Windows 10 Insider Preview (Version 10.0.17035 Build 17035)
• SDK version used: 1.5.2

Description of the issue:

Setting a reported property to null should remove that property, as I understand from the docs. It doesn't in some situations.

Code sample exhibiting the issue:

using Microsoft.Azure.Devices.Client;
using Microsoft.Azure.Devices.Shared;
using System;
using System.Threading.Tasks;

namespace IotHubClient
{
    class Program
    {
        static void Main(string[] args)
        {
            MainAsync(args).GetAwaiter().GetResult();
        }

        static async Task MainAsync(string[] args)
        {
            var client = DeviceClient.CreateFromConnectionString("Connection string here");

            await client.UpdateReportedPropertiesAsync(new TwinCollection
            {
                ["a"] = null
            });

            await client.UpdateReportedPropertiesAsync(new TwinCollection
            {
                ["a"] = new TwinCollection
                {
                    ["b"] = null
                }
            });

            await client.UpdateReportedPropertiesAsync(new TwinCollection
            {
                ["a"] = new TwinCollection
                {
                    ["b"] = null
                }
            });
        }
    }
}

Use breakpoints and observe the device twin after each call. The first call will erase a from the document root as expected. The second call is buggy and creates object a with key b, containing null, instead of creating an empty object (I expect b to be removed). The third call (assigning null to a key containing null) works as expected (removing b). It seems like the issue only repros when creating a new object with null values.

Somewhat related to #86 .

This affects me when I want to remove keys (right now I would have to first check if the object nesting the key exists before trying to remove it).

[tiagoshibata]

It repros in both reported and desired properties:

[CIPop]

Thanks for reporting @tiagoshibata !
We were able to repro the issue and now need to investigate to understand why this is happening.

[zolvarga]

@tiagoshibata

Update: It is a server side issue and I reported to the service team.
I will update you with the timeline.

Best Regards,
Zoltan

[timtay-microsoft]

Closing this issue because it isn't an SDK bug. The tests we disabled while the bug got fixed have been re-enabled, so I don't see a reason to keep this issue open

[az-iot-builder-01]

@tiagoshibata, @CIPop, thank you for your contribution to our open-sourced project! Please help us improve by filling out this 2-minute customer satisfaction survey