> wget https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml
> cp petstore.yaml petstore-optional-array-parameter.yaml
> $EDITOR petstore-optional-array-parameter.yaml # edit findByStatus operation with `required: false`
> diff -c petstore.yaml petstore-optional-array-parameter.yaml
*** petstore.yaml       2021-10-24 11:39:56.000000000 +0900
--- petstore-optional-array-parameter.yaml      2021-10-24 11:39:37.000000000 +0900
***************
*** 82,88 ****
          - name: status
            in: query
            description: Status values that need to be considered for filter
!           required: true
            style: form
            explode: false
            deprecated: true
--- 82,88 ----
          - name: status
            in: query
            description: Status values that need to be considered for filter
!           required: false
            style: form
            explode: false
            deprecated: true

> ./mvnw clean install
> java -jar modules/openapi-generator-cli/target/openapi-generator-cli.jar generate \
  -g scala-akka-http-server \
  -i petstore-optional-array-parameter.yaml \
  -o /var/tmp/scala-akka-http-server
> grep findByStatus -A4 /var/tmp/scala-akka-http-server/src/main/scala/org/openapitools/server/api/PetApi.scala
    path("pet" / "findByStatus") {
      get {
        parameters("status".as[String].?("new ListBuffer[String]() ")) { (status) =>
            petService.findPetsByStatus(status = status)
        }