code: public static String checkNotEmpty(String reference, @Nullable String message) throws IllegalArgumentException {
          if (reference == null || reference.isEmpty()) {
              throw new IllegalArgumentException(message == null ? "Null or empty value" : message);
          }
          return reference;
      }
docs: Check the nullity and emptiness of the given <code>reference</code>.
  
  @param reference reference to check
  @param message   exception message, can be <code>null</code>
  @return the given <code>reference</code>
  @throws IllegalArgumentException if the given <code>reference</code> is <code>null</code>