code: public static void notNull(Object obj, Supplier<String> message) {
      if (isNull(obj)) {
        throw new IllegalArgumentException(message.get());
      }
    }
docs: Asserts that the {@link Object} reference is not {@literal null}.
  
  The assertion holds if and only if the {@link Object} reference is not {@literal null}.
  
  @param obj {@link Object} reference to evaluate.
  @param message {@link Supplier} containing the message using in the {@link NullPointerException} thrown
  if the assertion fails.
  @throws java.lang.IllegalArgumentException if the {@link Object} reference is {@literal null}.
  @see java.lang.Object