Dapper.Contrib Nullable ID (#581)

[jurakovic]

Added support for Nullable ID property in Dapper.Contrib
Fix for issue #581

[NickCraver]

Can you please provide any tests illustrating the use case this fixes?

[jurakovic]

I have added InsertUserNullableId test
For some reason i cannot run tests in VS. No errors are shown so I don't know where is the problem :/
But I have tested it somehow outside of solution and it passes :)

[gilb195]

I've been experiencing this issue as well since I'm using a nullable int for the ID in my models. Thank you @jurakovic for this PR - would love to see this merged and fixed soon.

[NickCraver]

I can't speak to Contrib's future plans here and if this is a good fit, but please see #1658 - Dapper.Contrib is not located at https://github.com/DapperLib/Dapper.Contrib (separate from this repository).

Note: I based the Dapper.Contrib fork on the original codebase which hopefully makes porting pull requests against the main branch there much easier - the intent was to split, not throw away work the community wants to go with.