Ionic BaseService Issues

My BaseService provider on Ionic is giving an error.

import { Response } from '@angular/http';
import { Observable } from 'rxjs';
import { AngularFireList, AngularFireObject } from 'angularfire2/database';

const extractError = (error: Response | any): string => {
  // In a real world app, we might use a remote logging infrastructure
let errMsg: string;
if (error instanceof Response) {
    const body = error.json() || '';
    const err = body.error || JSON.stringify(body);
    errMsg = '${error.status} - ${error.statusText || ''} ${err}';
} else {
    errMsg = error.message ? error.message : error.toString();
}
console.error(errMsg);

return errMsg;

}

export abstract class BaseService {

protected handlePromiseError(error: Response | any): Promise<any> {
    return Promise.reject(extractError(error));
}

protected handleObservableError(error: Response | any): Observable<any> {
    return Observable.throw(extractError(error));
}

mapListKeys<T>(list: AngularFireList<T>): Observable<T[]> {
    return list
      .snapshotChanges()
      .map(actions => actions.map(action => ({ $key: action.key, ...action.payload.val() })));
}

mapObjectKey<T>(object: AngularFireObject<T>): Observable<T> {
    return object
      .snapshotChanges()
      .map(action => ({ $key: action.key, ...action.payload.val() }));
}

}

And gives this error in action.payload.val ()

[ts] Spreading types can be created only from object types. (property) Action > .payload: DatabaseSnapshot