fixing null Values<T>

[shervinw]

Based from the original null Values fix attempt from @nickevansuk, this PR just adds minor changes to solve the problem. Also see the problem origin.

Json.net has an internal method Newtonsoft.Json.Utilities.MiscellaneousUtils.ValueEquals(object objA, object objB) which utilises IEquatable to determine whether or not to write a property when DefaultValueHandling is specified.

The bulk of this fix occurs in Values{T1,T2}, Values{T1,T2, T3}, Values{T1,T2, T3, T4}, which contain method overrides specific to the issue.

I have also added an additional test that was previously removed.

[shervinw]

Also to note, running the generator causes the build to fail due to incompatible types, manually removed the following extract from Thing.cs to match master.

/// <summary>
/// Gets the context for the object, specifying that it comes from schema.org.
/// </summary>
[DataMember(Name = "@context", Order = 0)]
public override string Context => "http://schema.org";

The generator also modifies a bunch of properties to be of type Values<T> rather than OneOrMany<T>.

[RehanSaeed]

Thanks @shervinw for contributing! Have not forgotten about this PR. I'll try to take a look early next week.

[nickevansuk]

This looks exciting @shervinw! @RehanSaeed what do you think?

[RehanSaeed]

I now have time to take a look at this. I've just upgraded the project to use .NET Core 3.0 and also publish NuGet packages to the GitHub package registry.

Bravo! A simple change that seems to solve all issues. Not sure why I missed it.

Added you as a contributor on the main page as thanks.

[RehanSaeed]

Will release a major version update shortly.

[nickevansuk]

Great news guys! Well done @shervinw !

@RehanSaeed can I check that this lib will still be compatible with .NET Core 1 and 2? As our library built on top of it needs to be backwards compatible too...

[RehanSaeed]

Yes it will. We still target netstandard1.1 and netstandard2.0. I only use .NET Core 3 SDK to build, test and pack the package. It also gives us HTML test results.

[shervinw]

Awesome thanks Thanks Shervin

…

________________________________ From: Muhammad Rehan Saeed <notifications@github.com> Sent: Thursday, September 26, 2019 12:28:29 PM To: RehanSaeed/Schema.NET <Schema.NET@noreply.github.com> Cc: Shervin Williams <shervin@itpod.co.uk>; Mention <mention@noreply.github.com> Subject: Re: [RehanSaeed/Schema.NET] fixing null Values<T> (#84) Yes it will. We still target netstandard1.1 and netstandard2.0. I only use .NET Core 3 SDK to build, test and pack the package. It also gives us HTML test results. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub<#84?email_source=notifications&email_token=AC2CYAX757AT42FPDHTPA53QLSMF3A5CNFSM4IUASWU2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOD7VH2XQ#issuecomment-535461214>, or mute the thread<https://github.com/notifications/unsubscribe-auth/AC2CYATPRZD66BL5K3CR44DQLSMF3ANCNFSM4IUASWUQ>.