[BUG][java-vertx-web] Code generation issues with enum

Description

Found this issue with the java-vertx-web code generator. I've seen this in 5.1.1 and also in latest 6.0.1.
Code generation issue when enum is used in a parameter. For example:

...
paths:
  /pets:
    get:
      summary: List all pets
      operationId: ListPets
      tags:
        - pets
      parameters:
        - name: type
          $ref: '#/components/parameters/PetType'
...
components:
  schemas:
    PetType:
      maxLength: 20
      type: string
      enum:
        - CAT
        - DOG
        - BIRD
      description: Type of pet
  parameters:
    PetType:
      name: petType
      in: query
      required: false
      schema:
        $ref: '#/components/schemas/PetType'

Code generated is as follows:

    private void listPets(RoutingContext routingContext) {
        logger.info("listPets()");

        // Param extraction
..
        PetType petType = requestParameters.queryParameter("petType") != null ? requestParameters.queryParameter("petType").getPetType() : null;
...
}

Notice how the .getPetType() is generated incorrectly. Java compiler error is:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project openapi-java-vertx-web-server: Compilation failure
[ERROR] /C:/ADF/ws/expt/epl-1/generated/build/petstore/src/main/java/com/petstore/verticle/PetsApiHandler.java:[68,124] cannot find symbol
[ERROR]   symbol:   method getPetType()
[ERROR]   location: interface io.vertx.ext.web.validation.RequestParameter

This code needs manual fixing to following to compile:

        PetType petType = requestParameters.queryParameter("petType") != null ? PetType.valueOf(requestParameters.queryParameter("petType").getString()) : null;

openapi-generator version

5.1.1 to 6.0.1

OpenAPI declaration file content or url

$ java -ea -Xms1G -Xmx1G -server -jar openapi-generator-cli-6.0.1.jar generate -i petstore.yaml --model-package com.petstore.model --api-package com.petstore.verticle -g java-vertx-web -o java-vertx-web-petstore-1

Start by running the supplied openapi-generator-cli 6.0.1 command with the Petstore YAML and the java-vertx-web generator. Inspect the generated PetsApiHandler.java parameter extraction and compare the enum handling with the expected PetType.valueOf(...getString()) form. Done means the generated project compiles without manually editing the handler.