code: ContentCryptoScheme encryptionSchemeOf(Map<String,String> instructionFile) {
          if (instructionFile != null) {
              String cekAlgo = instructionFile.get(Headers.CRYPTO_CEK_ALGORITHM);
              return ContentCryptoScheme.fromCEKAlgo(cekAlgo);
          }
          ObjectMetadata meta = s3obj.getObjectMetadata();
          Map<String, String> userMeta = meta.getUserMetadata();
          String cekAlgo = userMeta.get(Headers.CRYPTO_CEK_ALGORITHM);
          return ContentCryptoScheme.fromCEKAlgo(cekAlgo);
      }
docs: Returns the original crypto scheme used for encryption, which may
  differ from the crypto scheme used for decryption during, for example,
  a range-get operation.
  
  @param instructionFile
  the instruction file of the s3 object; or null if there is
  none.