[BUG][JAVA] Java-Jersey2 generator creates "Accept:null" header

Created by: 40rn05lyv

Description

I use Jersey2 as generator for my REST, including DELETE operations that don't "accept" any body. As a result, I see that the generated code executes HTTP requests with header "Accept:null" that is not a valid header (because of "null" string).

openapi-generator version

I use openapi-generator-maven-plugin 4.2.3, but from what I see in source code this bug should be reproducible in the master too.

OpenAPI declaration file content or url

paths:
  /v2/something/{name}:
    delete:
      tags:
      - Repository
      summary: Delete something
      operationId: something_delete
      parameters:
      - name: paramone
        in: path
        required: true
        schema:
          type: string
      responses:
        "204":
          description: delete success or nothing to delete
        "401":
          description: not authenticated / invalid credentials
        "403":
          description: not authorized, the current user does not have the "repository"
            privilege
        "500":
          description: internal server error

Command line used for generation

pom.xml config:

                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>4.2.3</version>
...
                            <generatorName>java</generatorName>
                            <configOptions>
                                <java8>true</java8>
                                <library>jersey2</library>
                            </configOptions>
...

Steps to reproduce

See description, it's quite obvious.

Related issues/PRs

Not found

Suggest a fix

In file openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache change line from

Invocation.Builder invocationBuilder = target.request().accept(accept);

Invocation.Builder invocationBuilder = accept != null ? target.request().accept(accept) : target.request();

Also, need to check other generator for this problem.