Following implementation note for java.util.concurrent.ConcurrentMap.replaceAll talks about correctness properties thus it should be rethought in JDK 9 - may be it should be implSpec rather than implNote.

    /**
     * {@inheritDoc}
     *
     * @implNote This implementation assumes that the ConcurrentMap cannot
     * contain null values and get() returning null unambiguously means the key
     * is absent. Implementations which support null values
     * <strong>must</strong> override this default implementation.
     */
    @Override
    default void replaceAll(BiFunction<? super K, ? super V, ? extends V> function)