Hi,

I'm getting an exception java.lang.NoSuchMethodError: java.lang.Class.getPackageName()Ljava/lang/String; when creating an instance of AutoKonfig using AutoKonfig().withProperties(properties), which is coming from https://github.com/Nohus/AutoKonfig/blob/70035ebf9303dacacc6404507dbf873db2af5915/src/main/kotlin/dev/nohus/autokonfig/utils/SourceUtil.kt?rgh-link-date=2022-04-19T18%3A14%3A11Z#L17

I'm assuming this is because getPackageName() method was introduced in java 9 which makes it incompatible with java 8 or lower. Although you seem to have java compatibility set to 1.8 in build.gradle, it appears that you're actually using a later java version for compilation?

I've also made a PR that should fix this issue - #3 . The existing tests are passing fine, not sure if any new tests should be added though.

Currently, there is no way to create an "optional" setting with a null default value, as null is the same value used to indicate that a setting has no default value, and throwing an exception if the value is missing.

This forces you to define settings like this:

object ProxyConfig: Group("proxy") {
    val url by StringSetting("")
    val port by IntSetting(0)
}

And then validate them like this:

if (ProxyConfig.url.isNotBlank() && ProxyConfig.port > 0) {
    logger.warn { "Using SOCKS Proxy: ${ProxyConfig.url}:${ProxyConfig.port}" }
    proxy = ProxyBuilder.socks(ProxyConfig.url, ProxyConfig.port)
}

Clearly validating against null would be cleaner.

Suggested solutions:

• Change the default value of default to something other than null, this would require some new type for this and might break compatibility.
• Introduce a separate set of delegates: OptionalStringSetting, OptionalIntSetting. Ideally, the default value would have to be removed from the current settings so they are always required. But this could also make them more readable.