code: public String getSequence(Long beginPosition, Long endPosition)
  	{
  		byte[] sequenceByte = getSequenceByte(beginPosition, endPosition);
  		if (sequenceByte != null)
  			return new String(sequenceByte);
  		return null;
  	}
docs: Returns a subsequence string or null if the location
  is not valid.
  @param beginPosition the sequence begin position.
  @param endPosition the sequence end position.
  @return a subsequence string or null if the location is not valid.