code: public static StringBuilder appendMd5DigestAsHex(InputStream inputStream, StringBuilder builder)
          throws IOException {
          return appendDigestAsHex(MD5_ALGORITHM_NAME, inputStream, builder);
      }
docs: Append a hexadecimal string representation of the MD5 digest of the given inputStream to the given {@link
  StringBuilder}.
  
  @param inputStream the inputStream to calculate the digest over.
  @param builder the string builder to append the digest to.
  
  @return the given string builder.