[BUG] [Client] [Java] [Vertx] Current context may return NPE when creating new WebClient

Created by: ricardozanini

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

Hi!

While testing the generated client code for the petstore.yaml example, the ApiClient.java code is returning NPEs the first time it tries to create a WebClient reference. More specifically here: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache#L124-L132

Is there a reason to not use this.vertx.getOrCreateContext() instead? The vertx attribute is final. I can send a small PR to fix this, but I'd like to hear from the contributors first.

openapi-generator version

5.0.0

OpenAPI declaration file content or URL

Tested with petstore.yaml simple example.

Generation Details

Here's my plugin configuration:

<build>
    <plugins>
      <plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${version.openapi.generator}</version>
        <executions>
          <execution>
            <id>default</id>
            <goals>
              <goal>generate</goal>
            </goals>
            <configuration>
              <inputSpec>${project.basedir}/src/main/resources/petstore.yaml</inputSpec>
              <generatorName>java</generatorName>
              <library>vertx</library>
              <configOptions>
                <dateLibrary>java8</dateLibrary>
              </configOptions>
              <apiPackage>${project.groupId}.client</apiPackage>
              <modelPackage>${project.groupId}.client</modelPackage>
              <invokerPackage>${project.groupId}.client</invokerPackage>
              <generateApiTests>false</generateApiTests>
              <generateModelTests>false</generateModelTests>
              <generateModelDocumentation>false</generateModelDocumentation>
              <generateApiDocumentation>false</generateApiDocumentation>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

Steps to reproduce

1. Generate the Code
2. Run the tests with Junit5 and Vertx 3.9.5 (https://vertx.io/docs/3.9.5/vertx-junit5/java/)

Related issues/PRs

There's none

Suggest a fix

Replace Vertx.currentContext with this.vertx.getOrCreateContext()

By the way, I see that the server-side was upgraded to Vertx 4 (#7352 (closed)). Don't we need to upgrade the client code as well? I can also send a PR for this purpose.