Fix NullReferenceException in Rabbit.

[NachoEchevarria]

Summary of changes

We are getting the following NullReferenceException.

Error : Exception occurred when calling the CallTarget integration continuation.
System.NullReferenceException
at Datadog.Trace.ClrProfiler.AutoInstrumentation.RabbitMQ.PopulateBasicPropertiesHeadersIntegration.OnMethodEnd[TTarget,TReturn](TTarget instance, TReturn returnValue, Exception exception, CallTargetState& state)
at RabbitMQ.Client.Impl.Channel.PopulateBasicPropertiesHeaders[TProperties](TProperties basicProperties, Activity sendActivity, UInt64 publishSequenceNumber)

We can reproduce the issue with the following code:

BasicProperties property = default; -> NULL
var duckType = property.DuckCast<IBasicProperties>()!; -> duckType = NULL
duckType.Headers ??= new Dictionary<string, object>(); -> NullReferenceException

Reason for change

Implementation details

Test coverage

Other details

[andrewlock]

Thanks!

[andrewlock]

I think we could/should also change the definition of basicProperties above to this?

        TReturn basicProperties;

Alternatively, we could remove the else and change the definition to

        TReturn basicProperties = returnValue;

But I think the else is probably clearer

[NachoEchevarria]

Done!

[andrewlock]

Execution-Time Benchmarks Report ⏱️

Execution-time results for samples comparing the following branches/commits:

• This PR (7083)
• master

Execution-time benchmarks measure the whole time it takes to execute a program. And are intended to measure the one-off costs. Cases where the execution time results for the PR are worse than latest master results are shown in red. The following thresholds were used for comparing the execution times:

• Welch test with statistical test for significance of 5%
• Only results indicating a difference greater than 5% and 5 ms are considered.

Note that these results are based on a single point-in-time result for each branch. For full results, see the dashboard.

Graphs show the p99 interval based on the mean and StdDev of the test run, as well as the mean value of the run (shown as a diamond below the graph).

gantt
    title Execution time (ms) FakeDbCommand (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (68ms)  : 65, 70
     .   : milestone, 68,
    master - mean (67ms)  : 65, 70
     .   : milestone, 67,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (1,009ms)  : 985, 1033
     .   : milestone, 1009,
    master - mean (1,004ms)  : 983, 1024
     .   : milestone, 1004,

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gantt
    title Execution time (ms) FakeDbCommand (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (102ms)  : 100, 104
     .   : milestone, 102,
    master - mean (102ms)  : 100, 105
     .   : milestone, 102,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (697ms)  : 679, 715
     .   : milestone, 697,
    master - mean (696ms)  : 680, 713
     .   : milestone, 696,

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gantt
    title Execution time (ms) FakeDbCommand (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (89ms)  : 86, 92
     .   : milestone, 89,
    master - mean (89ms)  : 87, 91
     .   : milestone, 89,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (658ms)  : 634, 682
     .   : milestone, 658,
    master - mean (660ms)  : 630, 690
     .   : milestone, 660,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Framework 4.8) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (190ms)  : 186, 195
     .   : milestone, 190,
    master - mean (190ms)  : 186, 194
     .   : milestone, 190,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (1,113ms)  : 1089, 1137
     .   : milestone, 1113,
    master - mean (1,114ms)  : 1085, 1142
     .   : milestone, 1114,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET Core 3.1) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (270ms)  : 266, 275
     .   : milestone, 270,
    master - mean (269ms)  : 266, 272
     .   : milestone, 269,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (886ms)  : 855, 916
     .   : milestone, 886,
    master - mean (884ms)  : 851, 917
     .   : milestone, 884,

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gantt
    title Execution time (ms) HttpMessageHandler (.NET 6) 
    dateFormat  X
    axisFormat %s
    todayMarker off
    section Baseline
    This PR (7083) - mean (263ms)  : 260, 266
     .   : milestone, 263,
    master - mean (261ms)  : 258, 265
     .   : milestone, 261,

    section CallTarget+Inlining+NGEN
    This PR (7083) - mean (876ms)  : 839, 912
     .   : milestone, 876,
    master - mean (873ms)  : 836, 911
     .   : milestone, 873,

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[datadog-datadog-prod-us1]

Datadog Report

All test runs cf96970 🔗

✅ 2 Total Test Services: 0 Failed, 2 Passed

Test Services

Service Name	Failed	Known Flaky	New Flaky	Passed	Skipped	Total Time	Test Service View
dd-trace-dotnet	0	0	0	558030	4575	27h 0m 23.17s	Link
exploration_tests	0	0	0	22085	3	2m 12s	Link

[bouwkast]

Nice thanks!

[NachoEchevarria]

Thanks!