[BUG] [JAVA] Using an object to pass query params ends up using the toString of that class

Created by: mtohmaz

Description

When specifying the query parameters for an endpoint as an object and generate a Java SDK using openapi-generator-cli, it will actually use the class's toString as the query parameter values instead. For example, here is a sample config I have for openapi version 3.

paths:
  /my_endpoint:
    get:
      tags:
        - "MyEndpoint"
      operationId: "getMyEndpoint"
      parameters:
        - in: query
          name: queryParams
          explode: true
          schema:
            type: object
            properties:
              to:
                type: string
              from:
                type: string

After generating the java SDK and make a request like so:

QueryParams queryParams = new QueryParams();
queryParams.setTo("Person");
MyEndpointSuccessResponse result = apiInstance.getMyEndpoint(queryParams);

The request is received by my endpoint, but this is what the query params look like: {"query_params"=>"class QueryParams {\n to: Person\n from: null\n}"}

openapi-generator version

4.2.1-SNAPSHOT

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