@Override
  public boolean hasNext() {
    if (closed) {
      return false;
    }
    if (this.heap != null) {
      return (this.heap.peek() != null);
    }
    // Doing this way in case some test cases tries to peek directly
    return false;
  }
The MemStoreMergerSegmentsIterator extends MemStoreSegmentsIterator and performs the scan for
simple merge operation meaning it is NOT based on SQM
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreMergerSegmentsIterator.java