Added the possibility of null params for option types

[vycastor]

Hi all,

Experimenting lately my development with VSCode, I experimented that it can send null for any field, and ocaml-rpc doesn't support it. I propose here to support this feature at least for option types.

I'd like to write tests for that, but I don't know how to add them. Can you help me with it?

[mseri]

The behaviour of VSCode is a bit weird though, Some None -> None seems wrong. Maybe we should consider a mechanism to allow for some optional weakening of the rule.

Some None -> None is a join so it is noty that weird after all, it is weird to have a 'a option option :P

[mseri]

For tests, in this case I would probably keep them simple and add a jsonrpc call for this case to the tests/lib/json.ml file and the corresponding Rpc value to compare

[mseri]

@vycastor any update on testing this?