public static void ensureNotInstanceOf(String description, Object item, Class<?> type) {
        if ( type.isAssignableFrom(item.getClass())) {
            throw new IllegalArgumentException(description + " " + item + " should NOT be an instance of " + type +
                    " but is " + item.getClass());
        }
    }
Ensures that an item is not of a particular class

@param description a description of the item to be checked
@param item the item to check the type of
@param type the type the given item should NOT be instanceof
@throws IllegalArgumentException if the given item is of the wrong type
vespajlib/src/main/java/com/yahoo/protect/Validator.java