code: ByteArraySegment getPageKey() {
          ByteArraySegment r = this.pointer == null ? null : this.pointer.getKey();
          if (r == null && getPage().getCount() > 0) {
              r = getPage().getKeyAt(0);
          }
          return r;
      }
docs: Gets a ByteArraySegment representing the Page Key. A Page Key is the Key that the Page with which the page is
  registered in its parent. Most of the times this is the first Key in the Page, however if the first key is deleted,
  there may be disagreement (but the page key cannot change).
  
  @return The Page Key.