[BUG][Java] Generated code doesn't compile if the default value of an object is an empty object `{}`

Description

When generating a client package with the java generator using the library=native, if an object has a default value of {}, the generated code doesn't compile.
This might also be true for other library values but I didn't check.

openapi-generator version

7.7.0

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: Basic API
  description: A simple API that returns an object with a name and a value.
  version: 1.0.0

paths:
  /item:
    get:
      summary: Get an item
      description: Returns an object with a name and a value.
      responses:
        '200':
          description: Successful response
          content:
            application/json:
              schema:
                type: object
                properties:
                  name:
                    type: string
                  value:
                    $ref: '#/components/schemas/Value'
components:
  schemas:
    Value:
      type: object
      default: {}
      properties:
        optionalProperty:
          type: string
          description: This is an optional property.

Generation Details

openapi-generator-cli generate -i specs.yaml -c config.json -g java -o client

config.json:

{ "library": "native" }

Steps to reproduce

Run the command with the given specs.yaml and config.json
Then try to compile the code with cd client && mvn package
Compilation fails with the following error message:

client/src/main/java/org/openapitools/client/model/ItemGet200Response.java:[46,25] illegal initializer for org.openapitools.client.model.Value

The code contains:

...
  private Value value = {};
...

Reproduce the issue with specs.yaml and config.json, using the Java generator with library=native. Inspect the generated ItemGet200Response.java around the Value initializer, then run cd client && mvn package to confirm the failure. Done means the generated client compiles successfully when the schema default is an empty object.