openapi-generator does not generate JsonNullable<?> for Java Client

Question

The openapi generator should generate JsonNullable<?> type when a property is defined as nullable:true.

I've created the next repository to show the issue: https://github.com/robertop87/opengen

Basically when property defined in swagger.yml has nullable: true, like the next example:

openapi-generator version 7.3.0 (gradle plugin)

tag:
  type: string
  nullable: true

The generator should generate Java code as:

private JsonNullable<String> tag = JsonNullable.undefined();

But the current result is:

private String tag;

Please take a look in the example repository, maybe I'm doing something wrong or missing something.

Additionally I already reported this issue here: https://github.com/OpenAPITools/openapi-generator/issues/17873

I removed the nullable property, also make a combination with required, in any case I got the expected result.

My generator configuration in gradle.build file is:

tasks.register('generateClient', GenerateTask) {
    generatorName.set("java")
    inputSpec.set(swaggerFile.toString())
    outputDir.set(swaggerOutputDir)
    configOptions.set([dateLibrary: "java8", useJakartaEe: "true"])
}

Update 1:

The JsonNullable is being generated properly using

  generatorName.set("spring")

But this is to generate a server application, not a client.

Update 2: According docs there are extension to enable the expected generator behavior, in this case enabling x-is-jackson-optional-nullable: true should be enough, but the generator still doing the same.

Check latest commits in https://github.com/robertop87/opengen

Update 3:

When debugging the openapi-generatod source code, I noticed that JsonNullable is working fine, because the generator's library is configured as WEBCLIENT.

Additional note: x-is-jackson-optional-nullable was not needed in the configuration.

So I configured my generator like this:

tasks.register('generateClient', GenerateTask) {
    generatorName.set("java")
    library.set("webclient") // only with webclient the JsonNullable is generated properly
    inputSpec.set(swaggerFile.toString())
    outputDir.set(swaggerOutputDir)
    configOptions.set([
            dateLibrary: "java8",
            useJakartaEe: "true",
            openApiNullable: "true" // This is enabled by default
    ])
}

As result the JsonNullable were generated properly.

But, I'll test a bit more in client side if it's working as expected.