code: public static DataChecksum newDataChecksum( byte bytes[], int offset ) {
      if ( offset < 0 || bytes.length < offset + HEADER_LEN ) {
        return null;
      }
      
      // like readInt():
      int bytesPerChecksum = getIntFromBytes(bytes, offset + 1);
      return newDataChecksum( bytes[offset], bytesPerChecksum );
    }
docs: Creates a DataChecksum from HEADER_LEN bytes from arr[offset].
  @return DataChecksum of the type in the array or null in case of an error.