code: private int skipForward() {
          int numSkips = 0;
          _next = null;
          while (_iterator.hasNext() && getBlock(_next = _iterator.next()) != 0) {
              numSkips++;
              _next = null;
          }
          return numSkips;
      }
docs: This handles the edge case in which a client has explicity specified a changeId when writing and overwrote an exisiting delta.