code: public Charset getContentCharset() {
      return mediaType == null || mediaType.getCharsetParameter() == null
          ? Charsets.ISO_8859_1
          : mediaType.getCharsetParameter();
    }
docs: Returns the {@link Charset} specified in the Content-Type of this response or the {@code
  "ISO-8859-1"} charset as a default.
  
  @since 1.10