code: public final Composite start(CellName cellName) {
          CBuilder builder = cellNameType.builder();
          for (int i = 0; i < cellName.clusteringSize(); i++) {
              ByteBuffer component = cellName.get(i);
              builder.add(component);
          }
          return builder.build();
      }
docs: Returns the first possible cell name of those having the same clustering key that the specified cell name.
  
  @param cellName A storage engine cell name.
  @return The first column name of for {@code clusteringKey}.