By default, all enum sources must have a defined target. This can be disabled locally by adding @UseStrictEnums(false) to the mapper, or globally adding the following configuration to the Gradle build file

mappie {
    strictness {
        enums = false // Do not report an error if not all enum sources are mapped 
    }
}

Note that this might result in a NoWhenBranchMatchedException being thrown at runtime.