Harden convertToHttpParams against TypeError

[K-e-l-v-i-n-12]

I have noticed that the convertToHttpParams method is susceptible to undefined parameters. This can be verified using the following example:

public getCars(filter?: CarFilter): Observable<ResourceCollection<CarItem>> {
  const params = {
    ...filter
    // additional params...
  };
  return this.resourceHateoasService.getCollection(CarItem, { params });
}

This method is now called by a business service:

getCarsByPerson(manufacturer: string | undefined, personId: string): Observable<CarItem[]> {
  const filter = {
    manufacturer,
    personId
  } as CarFilter;
  return this.carResourceService.getCars(filter).pipe(
    catchError(() => { return of(new ResourceCollection<CarItem>()) }),
    map(page => page.resources)
  );
}

If a call is now made without a manufacturer, the following error is thrown:

ERROR TypeError: value is undefined
    convertToHttpParams lagoshny-ngx-hateoas-client.mjs:517
    convertToHttpOptions lagoshny-ngx-hateoas-client.mjs:540
    get lagoshny-ngx-hateoas-client.mjs:1623
    getResourceCollection lagoshny-ngx-hateoas-client.mjs:1653
    getCollection lagoshny-ngx-hateoas-client.mjs:2406
    getCars car-resource.service.ts:19

As a workaround, the filter can be created as follows:

const filter = {
  ...(manufacturer !== undefined && { manufacturer }),
  personId
} as CarFilter;

I would like ngx-hateoas-client to be able to handle undefined parameters in the future. I look forward to your feedback.