code: @SuppressWarnings("unchecked")
    private E borrowInternal() {
  
      if (this.size > 0) {
        E element = (E) this.pool[this.size];
        this.pool[this.size--] = null;
        return element;
      } else {
        return create();
      }
    }
docs: @see #borrow()
  
  @return the borrowed object.