@Override
      public boolean advance() {
        while (true) {
          if (this.currentIterator == null) {
            if (!this.entries.hasNext()) return false;
            this.currentIterator = this.entries.next().getValue().iterator();
          }
          if (this.currentIterator.hasNext()) {
            this.currentCell = this.currentIterator.next();
            return true;
          }
          this.currentCell = null;
          this.currentIterator = null;
        }
      }
Flatten the map of cells out under the CellScanner
@param map Map of Cell Lists; for example, the map of families to Cells that is used inside
           Put, etc., keeping Cells organized by family.
@return CellScanner interface over <code>cellIterable</code>
hbase-common/src/main/java/org/apache/hadoop/hbase/CellUtil.java