code: public static Identifier fromLong(long longValue, int desiredByteLength) {
          if (desiredByteLength < 0) {
              throw new IllegalArgumentException("Identifier length must be > 0.");
          }
          byte[] newValue = new byte[desiredByteLength];
          for (int i = desiredByteLength-1; i >= 0; i--) {
              newValue[i] = (byte) (longValue & 0xff);
              longValue = longValue >> 8;
          }
          return new Identifier(newValue);
      }
docs: Creates an Identifer backed by an array of length desiredByteLength
  @param longValue a long to put into the identifier
  @param desiredByteLength how many bytes to make the identifier
  @return