code: private String determineHashes(HashingFunction hashFunction) {
          if (isVirtual) {
              return null;
          }
          try {
              final File file = getActualFile();
              return hashFunction.hash(file);
          } catch (IOException | RuntimeException ex) {
              LOGGER.warn("Unable to read '{}' to determine hashes.", actualFilePath);
              LOGGER.debug("", ex);
          } catch (NoSuchAlgorithmException ex) {
              LOGGER.warn("Unable to use MD5 or SHA1 checksums.");
              LOGGER.debug("", ex);
          }
          return null;
      }
docs: Determines the SHA1 and MD5 sum for the given file.
  
  @param hashFunction the hashing function
  @return the checksum