docs: private static String getContentTypeEncoding(final String httpContentType) {
          String encoding = null;
          if (httpContentType != null) {
              final int i = httpContentType.indexOf(";");
              if (i > -1) {
                  final String postMime = httpContentType.substring(i + 1);
                  final Matcher m = CHARSET_PATTERN.matcher(postMime);
                  if (m.find()) {
                      encoding = m.group(1);
                  }
                  if (encoding != null) {
                      encoding = encoding.toUpperCase(Locale.ENGLISH);
                  }
              }
              if (encoding != null && (encoding.startsWith("\"") && encoding.endsWith("\"") || encoding.startsWith("'") && encoding.endsWith("'"))) {
                  encoding = encoding.substring(1, encoding.length() - 1);
              }
          }
          return encoding;
      }