Handling Nullable Types with option().converter()

[VEZE]

Context

I'm trying to create a custom converter for BuildType?, which I can implement successfully. However, I run into an issue when trying to use it with:

val buildType: BuildType? by option().converter(converter)

The problem is that option().converter() expects a non-nullable type, making it incompatible with my implementation.

Implementation

Here’s my current converter:

val convert: ValueTransformer<BuildType?> = { input ->
    when (input.lowercase()) {
        "release" -> Release
        "debug" -> Debug
        "debug-specific" -> DebugSpecific
        else -> null
    }
}

Real-World Use Case

In our CI pipeline, parameters are configured via a UI interface, and the build_type parameter may or may not be provided. The CLI command is executed as follows:

./cli command --build-type %build_type%

If build_type is not set, it remains empty, causing the command to fail. To handle this scenario, I need a custom converter that gracefully handles an empty value by returning null.

Question

Is there a recommended approach or workaround to make option().converter() work with nullable BuildType?, allowing it to accept empty values without causing an error?

Any insights or suggestions would be greatly appreciated! 🚀

[ajalt]

option().convert() doesn't allow null values because then you wouldn't be able to tell whether or not the option was specified. I would suggest showing the user an error when they specify an invalid value so they know they made a typo rather than continuing on silently. That's how the enum converter works.

However, if you really want to do that, you can use transformAll instead:

val buildType by option().transformAll {
    it.lastOrNull()?.let { input ->
        when (input.lowercase()) {
            "release" -> Release
            "debug" -> Debug
            "debug-specific" -> DebugSpecific
            else -> null
        }
    }
}

[VEZE]

In my case, it would require additional Bash scripts with logic to determine whether to add an option based on the provided value. Since we aim to migrate all logic to Kotlin, this approach doesn't work for us. ( Mean showing error to user ).
For my case, will be nice to have an option to treat empty string as null.