void addObject(Iterable<? extends Map.Entry<? extends IN_NAME, ?>> entries) {
        if (entries == this) {
            throw new IllegalArgumentException("can't add to itself.");
        }

        if (!addFast(entries)) {
            addObjectSlow(entries);
        }
    }
Only adds the specified {@code name} and {@code values}, and do not notify the changes via
{@link #onChange(CharSequence)}.
core/src/main/java/com/linecorp/armeria/common/StringMultimap.java