Fixed ID type deserialization

[hth313]

Deserialization of ID types caused an exception if the field was
nullable.

This corrects #244 and adds a test-case for it.

[xperiandri]

@hth313 is this already fixed? Can we close this PR?

[hth313]

I have no idea. I made a couple of PRs, some were merged but I do not think all of them. Not sure why and it was a long time ago. Looking at it now it seems that this was not merged, the misspelled "sring" is still there, but the actual fix does not match the code anymore. I really have no idea, I moved on, you can do what you feel is best.

[xperiandri]

As you can see I push this library forward. Soon we will have the latest GraphQL grammar support, CI&CD, solution template, etc.. So if you can check and update your PR I would appreciate that

[hth313]

It is good to see healthy open source projects. Sadly I will most likely not be able to update the PR as I work in very different dev stacks these days. I do not have needed tools and VMs installed for this anymore.

[xperiandri]

@hth313 add me to you fork repo as editor, please

[hth313]

You can just fork, clone or define a remote to it and pull things from it as needed.
The project is here: https://github.com/hth313-forks/FSharp.Data.GraphQL/tree/deserialization