[BUG] NodeJS OpenAPI client error on parse Object.keys(null) param

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

On NodeJS generated OpenAPI client when passing to a function a non-required parameter with value null the lib crashed with error
Cannot convert undefined or null to object

openapi-generator version

2.5.2

OpenAPI declaration file content or url

function setFlattenedQueryParams(urlSearchParams, parameter, key) {
    if (key === void 0) { key = ""; }
    if (typeof parameter === "object") {
        if (Array.isArray(parameter)) {
            parameter.forEach(function (item) { return setFlattenedQueryParams(urlSearchParams, item, key); });
        }
        else {
            Object.keys(parameter).forEach(function (currentKey) {
                return setFlattenedQueryParams(urlSearchParams, parameter[currentKey], "".concat(key).concat(key !== '' ? '.' : '').concat(c {snip}
            });
        }
    }

Generation Details

Steps to reproduce

1. Generate the lib with a function with a non-required param
2. Pass that param with value null

Related issues/PRs

Suggest a fix

https://github.com/OpenAPITools/openapi-generator/pull/14175

Start at the generated NodeJS client's setFlattenedQueryParams function shown in the issue and reproduce the call with a non-required parameter set to null. Confirm that the client no longer throws when handling that value; the suggested fix is in pull request 14175.