bom dia, o get esta dando erro na hora que vou definir a url

 constructor(){
        this._http = new HttpService();
    }

    static testWithAjax() {

        return new  Promise((resolve, reject) => {
             this._http
             .get('https://reqres.in/api/users/2')
             .then(form => {
                 document.querySelector('#nameTwo').innerHTML = `${form.id}`
             })
        });
    }

erro no console

Uncaught (in promise) TypeError: Cannot read property 'get' of undefined

get(url){
        return new Promise((resolve, reject) => {
            let xhr = new XMLHttpRequest();

            xhr.open('GET', url);

            xhr.onreadystatechange = () => {
                if (xhr.readyState == 4) {

                    if (xhr.status == 200) {

                        resolve(JSON.parse(xhr.responseText).data);

                    }
                }
            }
            xhr.send();
        });
    }