Boolean-like null values are not properly handled

Discord represents booleans in role tags using `null`, with `undefined` representing `false`. However, in Luau, there is no distinction between `null` and `undefined`, as `nil` serves as the universal placeholder. Consequently, the current handling of role tags requires either a custom `null` type or the conversion of `null` values to explicit booleans (`true`/`false`) using a custom JSON encoder/decoder.