code: public static byte[] decodeSequenceOptionalElement(byte[] element)
      {
          int index = 0;
  
          // check tag
          checkArgument((element[0] & 0xE0) == 0xA0, "Expected optional sequence element tag");
          index++;
  
          // read length
          int length = decodeLength(element, index);
          index += encodedLengthSize(length);
          checkArgument(length + index == element.length, "Invalid optional sequence element");
  
          return Arrays.copyOfRange(element, index, index + length);
      }
docs: Decodes a optional element of a sequence.