[BUG] [JAVA] Multipart requests in generated client contains class name

Description

I'm trying to upload a file and also specify an object containing metadata with regards to that file. When I create the requestBody content and generate the client, it creates a class for that object. When I create an object of that class and set the values of the metadata, I then pass it to the method making the API request. However, the request parameter for that object comes out as a string and contains the class name of the object. An exmaple of the resulting params:
Parameters: {"data"=>"class SentFileData {\n from: me\n to: someone\n}", "file"=>"file"}

openapi-generator version

4.2.1-SNAPSHOT

OpenAPI declaration file content or url

/sent_file:
  post:
    tags:
      - "SendFile"
    operationId: "sendFile"
    requestBody:
      content:
        multipart/form-data:
          schema:
            type: object
            properties:
              file:
                type: string
                format: binary
              data:
                type: object
                properties:
                  from:
                    type: string
                  to:
                    type: string
                  name:
                    type: string

Command line used for generation

docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli generate
-i ./local/swagger.yaml
-g java
-o ./local/java
-c ./local/config.json

Steps to reproduce

1. Generate the client using above command.
2. Import it into an existing project.
3. Use the code below to make a request to any endpoint (can be a mock server)

    SendFileApi apiInstance = new SendFileApi(defaultClient);
    File file = new File("/path/to/file"); // File | 
    SentFileData data = new SentFileData();
    data.setFrom("me");
    data.setTo("someone");
    try {
      SentFaxSuccessResponse result = apiInstance.sendFile(file, data);
      System.out.println(result);
    } catch (ApiException e) {
      System.err.println("Exception when calling SendFileApi#sendFile");
      System.err.println("Status code: " + e.getCode());
      System.err.println("Reason: " + e.getResponseBody());
      System.err.println("Response headers: " + e.getResponseHeaders());
      e.printStackTrace();
    }

Start by generating the Java client from the shown multipart/form-data declaration with the provided Docker command, then inspect the generated SendFileApi request handling for the data parameter. Reproduce the request using SentFileData and verify that the multipart part contains its from and to values rather than the class-name string.