code: public static void notEmpty(String string, String message) {
          if (string == null || string.length() == 0) {
              throw new IllegalArgumentException(message);
          }
      }
docs: <p>Validate that the specified argument string is
  neither <code>null</code> nor a length of zero (no characters);
  otherwise throwing an exception with the specified message.
  
  <pre>Validate.notEmpty(myString, "The string must not be empty");</pre>
  
  @param string the string to check
  @param message the exception message if invalid
  @throws IllegalArgumentException if the string is empty