Opentelemetry-dotnet: Traces are rejected by SignalFx because Root Span contains ParentSpanId=00000000

[ddiaz-relativity]

Bug Report

List of NuGet packages and
version that you are using (e.g. OpenTelemetry 0.4.0-beta.2):

• OpenTelemetry -Version 0.6.0-beta.7

Runtime version (e.g. net461, net48, netcoreapp2.1, netcoreapp3.1, etc.
You can find this information from the *.csproj file):

• netcoreapp3.1

Symptom

We were trying to export traces to SignalFx but they were rejected because the root span contained a property ParentSpanId equal to' 00000000' instead of 'null'.

We noticed this test was commented out which would identify the issue.
https://github.com/open-telemetry/opentelemetry-dotnet/blob/master/test/OpenTelemetry.Tests/Trace/TracerProviderSdkTest.cs#L47

This is the Span definition in the proto files https://github.com/open-telemetry/opentelemetry-proto/blob/master/opentelemetry/proto/trace/v1/trace.proto#L82

Reproduce

I used the example code from here and added the otlpExporter: https://github.com/open-telemetry/opentelemetry-dotnet/blob/master/examples/Console/TestConsoleExporter.cs#L43-L47

We will close this issue if:

• The repro project you share with us is complex. We can't investigate custom
  projects, so don't point us to such, please.
• If we can not reproduce the behavior you're reporting.

Additional Context

Add any other context about the problem here.

[cijothomas]

Opened an issue in runtime:
https://github.com/dotnet/runtime/issues/42456

(We may be able to workaround it in OpenTelemetry, but will wait to confirm if this is indeed a bug)

[cijothomas]

@ddiaz-relativity Were you using Otlp exporter? If yes, #1295 should fix this issue for you.
If you were writing own exporter, then do the similar workaround as 1295.

Let us know once you try this.

[ddiaz-relativity]

Comparing the output traces from the otel-dotnet library to the otel-Java library (As seen here https://github.com/Omnition/synthetic-load-generator) we see that the java-based Root spans have no parentSpanId.

So it seems signalfx would need to update their check on their side to something like this
if (activity.ParentSpanId.ToHexString() != EmptyActivitySpanId)

Or we can wait till https://github.com/dotnet/runtime/issues/42456 is fixed

[cijothomas]

@ddiaz-relativity Its fixed already. You can use our daily build from myget which would contain the fix