Plain class boolean parsing not working

[AndreasVolkmann]

The following test fails:

// Arrange
class Configuration(val headless: Boolean = false)

// Act
val config = Arkenv.parse<Configuration>(arrayOf("--headless", "true"))

// Assert
expectThat(config) { get { headless }.isTrue() }

This does work with delegates, just not with plain classes.

The parsing fails because it attempts to map the value, but no boolean mapping is available.