micronaut-examples | Example Projects Using Micronaut | Model View Controller library

The likely issue you're facing is because Groovy doesn't support Java method references or lambdas.

The first line is returning a lambda

Java: return key -> {

Groovy: return { key - >

That is using a groovy closure that takes the key as the argument.

Other places that use method references need to be converted

Java: .map(ConvertibleValues::of)

Groovy: .map({ values -> ConvertibleValues.of(values) })

It seems like you have most of that worked out, however you specifically asked about the map not being used. That is because you simply aren't passing it to the method.

values.reduce({all, keyValue-> vs values.reduce(map, {all, keyValue ->