final StringMultimap<IN_NAME, NAME> setIfAbsent(
            Iterable<? extends Map.Entry<? extends IN_NAME, String>> entries) {
        requireNonNull(entries, "entries");
        final Set<NAME> existingNames = names();
        if (!setIfAbsentFast(entries, existingNames)) {
            setIfAbsentSlow(entries, existingNames);
        }
        return this;
    }
Only sets the specified {@code name} and {@code value}, and do not notify the change via
{@link #onChange(CharSequence)}.
core/src/main/java/com/linecorp/armeria/common/StringMultimap.java