ExtendedCell getNextRow(final ExtendedCell cell) {
    ExtendedCell lowest = null;
    List<Segment> segments = getSegments();
    for (Segment segment : segments) {
      if (lowest == null) {
        lowest = getNextRow(cell, segment.getCellSet());
      } else {
        lowest = getLowest(lowest, getNextRow(cell, segment.getCellSet()));
      }
    }
    return lowest;
  }
@param cell Find the row that comes after this one. If null, we return the first.
@return Next row or null if none found.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/CompactingMemStore.java