code: public static String previous(CharSequence self) {
          StringBuilder buffer = new StringBuilder(self);
          if (buffer.length() == 0) throw new IllegalArgumentException("the string is empty");
          char last = buffer.charAt(buffer.length() - 1);
          if (last == Character.MIN_VALUE) {
              buffer.deleteCharAt(buffer.length() - 1);
          } else {
              char next = last;
              next--;
              buffer.setCharAt(buffer.length() - 1, next);
          }
          return buffer.toString();
      }
docs: This method is called by the -- operator for the class CharSequence.
  It decrements the last character in the given CharSequence. If the
  last character in the CharSequence is Character.MIN_VALUE it will be deleted.
  The empty CharSequence can't be decremented.
  
  @param self a CharSequence
  @return a String with a decremented character at the end
  @see #previous(String)
  @since 1.8.2