How to use the @delon/util.isEmpty function in @delon/util

checkContent(): void {
    if (!this.contentElement) {
      return ;
    }
    const el = this.contentElement.nativeElement as HTMLElement;
    const cls = `ad-desc-list__default`;
    if (!this.noDefault && isEmpty(el)) {
      this.renderer.addClass(el, cls);
    } else {
      this.renderer.removeClass(el, cls);
    }
  }

checkContent() {
    if (isEmpty(this.conTpl.nativeElement)) {
      this.renderer.setAttribute(this.conTpl.nativeElement, 'hidden', '');
    } else {
      this.renderer.removeAttribute(this.conTpl.nativeElement, 'hidden');
    }
  }

checkContent() {
    this.hasCon = !isEmpty(this.conTpl.nativeElement);
  }

checkContent() {
    const { conEl } = this;
    const def = this.default;
    if (!(def != null ? def : this.parent.default)) return;
    const el = conEl.nativeElement as HTMLElement;
    const cls = `sv__default`;
    if (el.classList.contains(cls)) {
      el.classList.remove(cls);
    }
    if (isEmpty(el)) {
      el.classList.add(cls);
    }
  }
}

checkContent(): void {
    const el = this.contentElement.nativeElement;
    const cls = `${prefixCls}__item-empty`;
    if (isEmpty(el)) {
      this.ren.addClass(el, cls);
    } else {
      this.ren.removeClass(el, cls);
    }
  }