private void addObjectSlow(Iterable<? extends Map.Entry<? extends IN_NAME, ?>> entries) {
        // Slow copy
        for (Map.Entry<? extends IN_NAME, ?> e : entries) {
            addObject(e.getKey(), e.getValue());
        }
    }
Invoked when all values are cleared.
core/src/main/java/com/linecorp/armeria/common/StringMultimap.java