Angular 4: "Http failure response for (unknown URL): 0 Unknown Error"

I am trying to consume an API URL. I am calling the API with the below code.

import {HttpClient, HttpClientModule, HttpParams} from "@angular/common/http";

@Injectable()
export class PropertyPrefService {

    constructor(private http: HttpClient,
                private configurationService:Configuration) {}

    public searchProjects(propFilter:string):any{
        let temp:any;
        const options = propFilter ?
        {
            params: new HttpParams().set('query', propFilter)
        } : {};

        return this.http.get<any>(this.configurationService.propertySystemApiUrl, options)
                    .subscribe((results:any) => {
                        console.log(results);
                    });
    }

In the Angular code I am not getting any response and am getting an error:

Http failure response for (unknown url): 0 Unknown Error".

However, when I make a request if I open up developer tools on Chrome, I see that the response is received from the server.

The URL is the "https://..." URL and not "http://...".

The problem is Angular Universal used Express, and the security validates the SSL certificate to the server; I used a self-signed SSL certificate.

The solution is to add NODE_TLS_REJECT_UNAUTHORIZED=0 to your environment to disable the SSL verification in Node.js. You should only set this in development; in production it is very risky.

Quoting Sander Elias on Google Groups:

"Error 0 is what you get when the request does not go out. Most common cause of this is that CORS is not configured correctly on the server. Let me rephrase that to: In 98% of the cases, this is a server side issue."