JsonNull return false when comparing against null

[henrikse55]

I'ved modified JsonNulls comparison methods to return false when
compared against null, the matching test have also been updated
in change

Fix #820

[dnfclas]

All CLA requirements met.

[henrikse55]

I do not believe the current tests which are failing are related to the changes I made as it network timeouts.

I also have a couple of questions as this is my first PR:

As it's just a timeout, should the failed tests be rerun?
When I think it's ready for review, should I tag the issuer?

@ahsonkhan

[ahsonkhan]

As it's just a timeout, should the failed tests be rerun?

Yes. However, what I tend to do (and encourage) is that I do a cursory search of the test failure/exception in the repo to see if an issue already exists tracking the intermittent failure, and if not, then file one, so that it gets tracked and resolved. Here are some examples: https://github.com/dotnet/corefx/issues/42583, https://github.com/dotnet/corefx/issues/42077, https://github.com/dotnet/corefx/issues/41881

When I think it's ready for review, should I tag the issuer?

Generally, you'd tag the area owners to help review the PR:
https://github.com/dotnet/runtime/blob/master/docs/area-owners.md

I am happy to look it over and provide feedback.

[ahsonkhan]

Other than updating xml doc comments, looks good.

[ahsonkhan]

I do not believe the current tests which are failing are related to the changes I made as it network timeouts.

Right, the test failure in CI is unrelated: https://github.com/dotnet/corefx/issues/20069#issuecomment-566292587

[henrikse55]

I have updated the XML docs and this should be ready for a review
@ahsonkhan @steveharter

The test failure looked unrelated to me and I've commented on #702

[ahsonkhan]

Thanks for fixing this @henrikse55 - let me know if you are interested in picking up other issues :)

https://github.com/dotnet/runtime/issues?q=is%3Aopen+is%3Aissue+label%3Aarea-System.Text.Json+label%3Aup-for-grabs
https://github.com/dotnet/corefx/issues?q=is%3Aopen+is%3Aissue+label%3Aarea-System.Text.Json+label%3Aup-for-grabs