TS2769 No overload matches this call

[rosemadder]

I'm looking at a tutorial on the utubus, like adding token in response. There's a service where they get token

  get token (): string | null {
    const fbTokenExp = localStorage.getItem('fb-token-exp');
    if (fbTokenExp) {
      const expDate = new Date(fbTokenExp);
      if ( new Date > expDate ) {
        this.logout()
        return null
      }
      return localStorage.getItem('fb-token')
    }
    return null;
  }

and intercept where the addition token occurs

intercept(req: import("@angular/common/http").HttpRequest<any>,
            next: import("@angular/common/http").HttpHandler): import("rxjs").Observable<import("@angular/common/http").HttpEvent<any>> {
if (this.auth.isAuthenticated()) {
  req = req.clone({
    setParams: {
      auth: this.auth.token
    }
  })
}

IDEA swears on this line

auth: this.auth.token

He says

TS2769: No overload matches this call.   Overload 1 of 3, '(update: { headers?: HttpHeaders | undefined; context?: HttpContext | undefined; reportProgress?: boolean | undefined; params?: HttpParams | undefined; ... 6 more ...; setParams?: { ...; } | undefined; }): HttpRequest<...>', gave the following error.     Type 'string | undefined' is not assignable to type 'string'.       Type 'undefined' is not assignable to type 'string'.   Overload 2 of 3, '(update: { headers?: HttpHeaders | undefined; context?: HttpContext | undefined; reportProgress?: boolean | undefined; params?: HttpParams | undefined; ... 6 more ...; setParams?: { ...; } | undefined; }): HttpRequest<...>', gave the following error.     Type 'string | undefined' is not assignable to type 'string'.       Type 'undefined' is not assignable to type 'string'.

I don't know how to fix it.

[Demir]

SetParams has a type:

{
 [param: string]: string;
}

You're most likely to transmit a meaning that can be undefined either by this.auth itself or by its properties this.auth.token.

Check whether the properties exist.

if (this.auth && this.auth.token) {
  req = req.clone({
    setParams: {
      auth: this.auth.token
    }
  })
}

Or use the operator. ! If you're sure there's a characteristic

if (this.auth.isAuthenticated()) {
    req = req.clone({
      setParams: {
        auth: this.auth!.token!
      }
    })
 }