public void addPresenceFlag(final @NonNull CommandFlag<?> flag) {
        ((List<Object>) this.flagValues.computeIfAbsent(
                flag.name(),
                $ -> new ArrayList<>()
        )).add(FLAG_PRESENCE_VALUE);
    }
Indicate that a presence flag was supplied

@param flag Flag instance
cloud-core/src/main/java/org/incendo/cloud/parser/flag/FlagContext.java