Allows nullable fields to be ignored during JSON deserialization

[RecklessBoon]

I have had some users provide some error messages like the following (account info redacted since it's irrelevant)

[ERROR]: Failed to process event! Error converting value {null} to type 'DiscordRPC.User+PremiumType'. Path 'user.premium_type'.
[ERROR]: Data: {"cmd":"DISPATCH","data":{"v":1,"config":{"cdn_host":"cdn.discordapp.com","api_endpoint":"//discord.com/api","environment":"production"},"user":{"id":"==REDACTED==","username":"==REDACTED==","discriminator":"==REDACTED==","avatar":"==REDACTED==","avatar_decoration":null,"bot":false,"flags":32,"premium_type":null}},"evt":"READY","nonce":null}

I have not been able to replicate this issue, however according to the documentation on the Discord Developer Portal - Documentation | Users Resource section, there are a handful of fields that can come in as null. This should make the library closer to spec and hopefully alleviate the issues my users are facing. Let me know if you want to discuss or if you have some way to test this before merging and releasing.

Thanks!

[dowmeister]

Fix confirmed. Had a user today reporting this, this PR fix it

[Lachee]

Thank you for your contribution. This is now released in v1.1.1 ✨🌟 🎉