code: public static void notEmpty(final String aString, final String argumentName) {
  
          // Check sanity
          notNull(aString, argumentName);
  
          if (aString.length() == 0) {
              throw new IllegalArgumentException(getMessage("empty", argumentName));
          }
      }
docs: Validates that the supplied object is not null, and throws an IllegalArgumentException otherwise.
  
  @param aString      The string to validate for emptyness.
  @param argumentName The argument name of the object to validate.
  If supplied (i.e. non-{@code null}), this value is used in composing
  a better exception message.