How to use the @material/mwc-base/base-element.classMap function in @material/mwc-base

protected render() {
    return html`
      <header class="mdc-top-app-bar ${classMap(this.barClasses)}">
      <div class="mdc-top-app-bar__row">
        <section id="navigation" class="mdc-top-app-bar__section mdc-top-app-bar__section--align-start">
          
          <span class="mdc-top-app-bar__title"></span>
        </section>
        <section role="toolbar" id="actions" class="mdc-top-app-bar__section mdc-top-app-bar__section--align-end">
          
        </section>
      </div>
    </header>
    <div class="${classMap(this.contentClasses)}">
      
    </div>
    `;
  }

protected render() {
    return html`
      <header class="mdc-top-app-bar ${classMap(this.barClasses)}">
      <div class="mdc-top-app-bar__row">
        <section id="navigation" class="mdc-top-app-bar__section mdc-top-app-bar__section--align-start">
          
          <span class="mdc-top-app-bar__title"></span>
        </section>
        <section role="toolbar" id="actions" class="mdc-top-app-bar__section mdc-top-app-bar__section--align-end">
          
        </section>
      </div>
    </header>
    <div class="${classMap(this.contentClasses)}">
      
    </div>
    `;
  }