[BUG] [C Client] incorrect generate "object_convertToJSON" function

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

I use OpenApi3 generator (Openapi-generator-cli-4.1.0) for C client, and found not for clean functional for me.

So, I have some json template where I plan to use "payload" like addition parameter (json Object type) for my functionality:

...
"data": {
"type": "object",
"properties": {
"message": {
"type": "string",
"minLength": 1,
"maxLength": 1024,
"description": "human-readable event description"
},
"payload": {
"type": "object",
"description": "(optional) Additional data, some object/property should be added, integer/string/array/object",
"properties": {}
}
},
....

after generation we have object.h and object.c files for working with object_t type.

Please to correct my if I am wrong.
For make "object" type need to do something like:

object_t* _tmp = object_create();
cJSON* obj = object_convertToJSON(_tmp);
if(cJSON_AddNumberToObject(obj, "value", 123)){
return true;
}

but currently looks like that function:"object_convertToJSON" not fully correct
or maybe my json template wrong?

cJSON *object_convertToJSON(object_t *object) {
    cJSON *item = cJSON_CreateObject();

    return item;
fail:
    cJSON_Delete(item);
    return NULL;
}

I fix this issue internally, like:

cJSON *object_convertToJSON(object_t *object) {
    **//cJSON *item = cJSON_CreateObject();**
    return (cJSON *)object;
}
...
cJSON * _tmp = cJSON_CreateObject();
bla-bla...

openapi-generator version

Openapi-generator-cli-4.1.0

OpenAPI declaration file content or url

Command line used for generation

Steps to reproduce

Related issues/PRs

Suggest a fix

Start by reproducing the report with OpenAPI Generator CLI 4.1.0 and the described OpenAPI 3 object schema. Inspect the generated object.c and object.h, focusing on object_convertToJSON; the fix is complete when generated C code correctly serializes the object payload without requiring the reported manual workaround.