code: public static Mode getUMask(@Nullable String confUmask) {
      int umask = Constants.DEFAULT_FILE_SYSTEM_UMASK;
      if (confUmask != null) {
        if ((confUmask.length() > 4) || !isValid(confUmask)) {
          throw new IllegalArgumentException(ExceptionMessage.INVALID_CONFIGURATION_VALUE
              .getMessage(confUmask, PropertyKey.SECURITY_AUTHORIZATION_PERMISSION_UMASK));
        }
        int newUmask = 0;
        int lastIndex = confUmask.length() - 1;
        for (int i = 0; i <= lastIndex; i++) {
          newUmask += (confUmask.charAt(i) - '0') << 3 * (lastIndex - i);
        }
        umask = newUmask;
      }
      return new Mode((short) umask);
    }
docs: Gets the file / directory creation umask.
  
  @param confUmask the string representation of umask
  @return the umask {@link Mode}