fix: static initialisers to avoid side effects in the JSON constructors

[sp00m]

As the title says :)

[wboereboom]

Hey @sp00m ,
Thanks a lot for contributing to our repository.
Could you please elaborate on the side effects you are trying to avoid?

Kind Regards,
Wouter
Adyen

[sp00m]

Hey @wboereboom,

The previous code relied on an instance initializer block to set a static variable, which is a side-effect: as the block executes each time a new instance is created, each new instance of JSON will overwrite the static gson instance. That's also the reason why you had to have new JSON(); statements scattered a bit everywhere I suppose.

Using a static block instead will get rid of this oddity and ensure gson is set only once: when the class first loads (unless JSON.setGson(...) is explicitly called again obviously).

Hope that makes sense. It's rather minor for sure, but I just came across it and the fix was rather quick, so I thought why not contributing :)

[wboereboom]

Great contribution @sp00m!

Thank you very much for taking the time to provide this quality-of-life change for the Library 🎉

Kind Regards,
Wouter
Adyen