Ionic 3 – Type '{}' is not assignable to type – Magento

Trying to figure out this error. I am attempting to call on an API, and map the JSON data from the API call to a CurrencyModel. No issues with that, but when I am calling on a method that returns an observable (as it is waiting for two other API calls), it’s throwing the following error to the provider property:

Type ‘{}’ is not assignable to type ‘CurrencyModel’.

src/models/currency.ts

export class CurrencyModel{
    private _base_currency_code: string;
    private _base_currency_symbol: string;
    private _default_display_currency_code: string;
    private _default_display_currency_symbol: string;
    private _available_currency_codes: Array<string> = [];
    private _exchange_rates: Array<CurrencyExchangeRateModel> = [];
    //extension attributes

    get base_currency_code(): string{
        return this._base_currency_code;
    }

    set base_currency_code(value: string){
        this._base_currency_code = value;
    }

    get base_currency_symbol(): string{
        return this._base_currency_symbol;
    }

    set base_currency_symbol(value: string){
        this._base_currency_symbol = value;
    }

    get default_display_currency_code(): string{
        return this._default_display_currency_code;
    }

    set default_display_currency_code(value: string){
        this._default_display_currency_code = value;
    }

    get default_display_currency_symbol(): string{
        return this._default_display_currency_symbol;
    }

    set default_display_currency_symbol(value: string){
        this._default_display_currency_symbol = value;
    }

    get available_currency_codes(): Array<string>{
        return this._available_currency_codes;
    }

    getAvailableCurrencyCode(key: number): string{
        return this.available_currency_codes[key];
    }

    set available_currency_codes(value: Array<string>){
        this._available_currency_codes = value;
    }

    setAvailableCurrencyCode(value: string): void{
        this.available_currency_codes.push(value);
   }

    get exchange_rates(): Array<CurrencyExchangeRateModel>{
        return this._exchange_rates;
    }

    getExchangeRate(key: number): CurrencyExchangeRateModel{
        return this.exchange_rates[key];
    }

    set exchange_rates(value: Array<CurrencyExchangeRateModel>){
        this._exchange_rates = value;
    }

    setExchangeRate(value: CurrencyExchangeRateModel): void{
        this.exchange_rates.push(value);
    }

    constructor(response?: any){
        if(response){
            this.base_currency_code = response.base_currency_code;
            this.base_currency_symbol = response.base_currency_symbol;
            this.default_display_currency_code = response.default_display_currency_code;
            this.default_display_currency_symbol = response.default_display_currency_symbol;
            this.available_currency_codes = response.available_currency_codes ;

            if(response.exchange_rates){
                for(let rate of response.exchange_rates){
                    this.setExchangeRate( new CurrencyExchangeRateModel(rate) );
                }
            }
        }
    }
}

src/providers/store/store.ts

import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Platform } from 'ionic-angular';

import { CurrencyModel } from '../../models/store/currency';

import { Observable } from 'rxjs/Observable';
import { forkJoin } from "rxjs/observable/forkJoin";
import { map } from 'rxjs/operators';

@Injectable()

export class StoreProvider {
    private apiUrl:string;

    // Defaults
    config: ConfigModel;
    countries: Array<CountryModel> = [];
    currency: CurrencyModel;

    constructor(public http: HttpClient){}

    readCurrency(): Observable<CurrencyModel>{
        return this.http.get<CurrencyModel>(this.apiUrl + '/directory/currency').pipe(
            map(data => new CurrencyModel(data))
        );
    }

    readConfig(): any{
        return this.http.get(this.apiUrl + '/store/storeConfigs');
    }

    //readCountries is the same, just different url

    getProperties(): Observable<boolean>{
        return Observable.create(observer => {
            let requests: Array<any> = [
                this.readConfig(),
                this.readCountries(),
                this.readCurrency()
            ];

            forkJoin(requests).subscribe(data => {

                this.config = this.getConfig(data[0][0]);
                this.countries = this.getCountries(data[1]);
                this.currency = data[2]; // Problem area

                observer.next(true);
            }, err => {
                observer.error(err);
            });
        });
    }
}

Purpose with the getProperties is to get data from the website that will need to be loaded first before anything else.

Data structure of response (Magento 2 Currency)

{
    "base_currency_code": "string",
    "base_currency_symbol": "string",
    "default_display_currency_code": "string",
    "default_display_currency_symbol": "string",
    "available_currency_codes": [
        "string"
    ],
    "exchange_rates": [
        {
            "currency_to": "string",
            "rate": 0,
            "extension_attributes": {}
        }
    ],
    "extension_attributes": {}
}

EDIT: Added the JSON data structure and CurrencyModel