Custom ConditionalGenericConverter annotation doesn't convert parameters in Spring GraphQL - spring

Question

I have a REST API developed in Spring and now I'm learning how to use GraphQL in my Spring project so I'm "translating" my REST endpoints to GraphQL queries.
Just to give some background on what I'm trying to do, I will show how one of my REST controllers look like (code in Kotlin):
Rest Controller
#RestController
#RequestMapping("countries")
class CountryController(private val countryService: CountryService) {
#GetMapping("{code}")
fun findByCode(#PathVariable #Uppercase code: String): Country {
return countryService.findByCode(code)
}
}
It's basically an endpoint that fetches a country based on a code. For example /countries/bra will fetch information about the country Brazil.
In the code above there's also a custom annotation called #Uppercase. This annotation extends ConditionalGenericConverter and the only thing it does is to take the code parameter and convert it to uppercase. This is the code for this annotation:
#Uppercase implementation
#Target(AnnotationTarget.VALUE_PARAMETER)
annotation class Uppercase
#Component
class UppercaseConverter : ConditionalGenericConverter {
override fun matches(sourceType: TypeDescriptor, targetType: TypeDescriptor): Boolean {
return targetType.getAnnotation(Uppercase::class.java) != null
}
override fun getConvertibleTypes(): MutableSet<ConvertiblePair>? {
return mutableSetOf(ConvertiblePair(String::class.java, String::class.java))
}
override fun convert(source: Any?, sourceType: TypeDescriptor, targetType: TypeDescriptor): String {
return (source as String).uppercase()
}
}
Everything works as expected in the code above and the code parameter is always converted to uppercase if I use the #Uppercase annotation in my REST controller.
Now I created a similar controller for Spring GraphQL that looks like this:
GraphQL Controller
#Controller
class CountryResolver(private val countryService: CountryService) {
#QueryMapping(name = "country")
fun findByCode(#Argument #Uppercase code: String): Country {
return countryService.findByCode(code)
}
}
And my GraphQL is executed properly with the code above, except that the parameter code is not converted to uppercase when I use my custom annotation #Uppercase. It seems that my custom annotation only works with #PathVariable in the REST controller, but it doesn't with #Argument in the GraphQL controller.
Any idea why on how to make it work with GraphQL as well? Thanks in advance!