code: public Revision get(final int revisionIndex)
  	{
  		if (this.storage.containsKey(revisionIndex)) {
  
  			ChronoStorageBlock block = this.storage.get(revisionIndex);
  			return block.getRev();
  		}
  		return null;
  	}
docs: Returns the revision of the specified chrono storage block.
  
  @param revisionIndex
  chronological order index
  @return