[BUG] [typescript-angular]: objects as query parameters break when fields are null

Created by: daniel-frak

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?

Description

When using the "objects as query parameter" support introduced in #4407, NULL fields cause an exception TypeError: Cannot convert undefined or null to object in the addToHttpParamsRecursive function of the generated service.

openapi-generator version

4.2.3

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: Test API
  version: v0.0.1
servers:
- url: http://localhost:8080
paths:
  "/myobjects/filtered":
    get:
      operationId: findAllByFilter
      parameters:
      - name: filter
        in: query
        required: true
        schema:
          "$ref": "#/components/schemas/MyObjectFilter"
      responses:
        '200':
          description: default response
          content:
            "*/*":
              schema:
                type: "string"
components:
  schemas:
    MyObjectFilter:
      type: object
      properties:
        query:
          type: string
        type:
          type: string
          enum:
          - TYPE1
          - TYPE2

Command line used for generation

openapi-generator generate -g typescript-angular -o .generated -i .swagger-spec.json

Steps to reproduce

1. Generate the code and copy it to an Angular application
2. Create a new MyObjectFilter with query==null:

const filter = {
  query: null,
  type: "TYPE1"
};

3. Try to use the service:

this.myObjectService.findAllByFilter(myObjectFilter)

Related issues/PRs

None found.

Suggest a fix

I have found that adding a NULL-check in the generated addToHttpParamsRecursive method seems to fix the issue:

private addToHttpParamsRecursive(httpParams: HttpParams, value: any, key?: string): HttpParams {
  if(value == null) {
    return httpParams;
  }
  // Original code starts here...
}