Response to preflight request doesn't pass access control check


I have an app am working on. It worked fine for some request i made to the server and of late I get this error
Response to preflight request doesn’t pass access control check: No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘null’ is therefore not allowed access.
I have a working request with the same method I used but now can’t figure out what when wrong.

    * User Authentication Authorizer Bearer
    this.requestOptions = new RequestOptions({
            headers: new Headers({
                'Authorization': `Bearer ${this.authService.getAuthUserToken()}`