@Override
    public final void forEach(BiConsumer<NAME, String> action) {
        requireNonNull(action, "action");
        for (Map.Entry<NAME, String> e : this) {
            action.accept(e.getKey(), e.getValue());
        }
    }
Validates the given user-specified {@code value}.
core/src/main/java/com/linecorp/armeria/common/StringMultimap.java