[BUG][Java][jersey2] ApiClient.setUserAgent does not set userAgent

Description

Error Prone fails compilation of project which includes generated ApiClient.java with error:

[SelfAssignment] Variable assigned to itself
(see https://errorprone.info/bugpattern/SelfAssignment)
Did you mean 'this.userAgent = userAgent;'?

@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen", date = "2021-02-12T13:57:28.286366700+01:00[Europe/Paris]")
public class ApiClient {
...
  protected String userAgent;
...
  /**
   * Set the User-Agent header's value (by adding to the default header map).
   * @param userAgent Http user agent
   * @return API client
   */
  public ApiClient setUserAgent(String userAgent) {
    userAgent = userAgent;
    addDefaultHeader("User-Agent", userAgent);
    return this;
  }
...

openapi-generator version

openapi-generator-maven-plugin version 5.0.1

Steps to reproduce

Generate a Java jerrsey2 client using the following configuration

<plugin>
  <groupId>org.openapitools</groupId>
  <artifactId>openapi-generator-maven-plugin</artifactId>
  <version>5.0.1</version>
  <executions>
    <execution>
      <goals>
        <goal>generate</goal>
      </goals>
      <configuration>
        <inputSpec>${project.basedir}/src/main/resources/vdx-swagger.yaml</inputSpec>
        <generatorName>java</generatorName>
        <library>jersey2</library>
        <modelNamePrefix>Vdx</modelNamePrefix>
        <modelPackage>dk.sundhed.ehealth.futvdx2fhir.api.model</modelPackage>
        <generateApis>false</generateApis>
        <generateModelTests>false</generateModelTests>
        <output>${project.build.directory}/generated-sources</output>
        <configOptions>
          <dateLibrary>legacy</dateLibrary>
          <caseInsensitiveResponseHeaders>true</caseInsensitiveResponseHeaders>
        </configOptions>
      </configuration>
    </execution>
  </executions>
</plugin>

Suggest a fix

  /**
   * Set the User-Agent header's value (by adding to the default header map).
   * @param userAgent Http user agent
   * @return API client
   */
  public ApiClient setUserAgent(String userAgent) {
    this.userAgent = userAgent;
    addDefaultHeader("User-Agent", userAgent);
    return this;
  }

Start with the Java jersey2 generator templates or entry points that produce ApiClient.java, using the provided Maven configuration to reproduce the generated setter. Confirm that the generated method assigns the instance field rather than the parameter to itself, then regenerate a client and verify the resulting Java source compiles without the Error Prone SelfAssignment error.