JAVA/Swagger-codegen-maven-plugin : explode param not taken into account

Description

explode option is note taken into account when generating client.

For the following operation :

"/operation/{operationId}": {
  "get": {
    "operationId": "retrieveOperationData",
    "parameters": [
      {
        "name": "allParams",
        "in": "query",
        "required": true,
        "style": "form",
        "schema": {
          "type": "object",
          "additionalProperties": {
            "type": "string"
          }
        }
      }
    ],
    "responses": {
      "200": {
        "description": "OK",
        "content": {
          "*/*": {
            "schema": {
              "$ref": "#/components/schemas/ModelReturn"
            }
          }
        }
      }
    }

Api client generated with swagger-codegen-maven-plugin generates th following request:
http://localhost:7999/operation/4?allParams=%7BadditionalProp1=myString1,%20additionalProp2=myString2,%20additionalProp3=myString3%7D

Swagger-ui on api generate the correct URL:

http://localhost:7999/operation/4?additionalProp1=myString1&additionalProp2=myString2&additionalProp3=myString3

with the following allParams query parameter value :
{
"additionalProp1": "myString1",
"additionalProp2": "myString2",
"additionalProp3": "myString3"
}

Is explode param really managed?

Many thanks to all.

Swagger-codegen version

version 3.0.23

Swagger declaration file content or url

json file use for both generation:
openapi.txt

Command line used for generation

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

Start with the supplied OpenAPI declaration and reproduce the generated Java client request through swagger-codegen-maven-plugin version 3.0.23. Trace how the object-valued allParams query parameter is serialized, then verify that explode produces separate additionalProp query parameters rather than one encoded object value.