src/main/java/org/jivesoftware/smack/util/collections/AbstractReferenceMap.java
public Set<K> keySet() {
        if (keySet == null) {
            keySet = new ReferenceKeySet<K, V>(this);
        }
        return keySet;
    }
public Set<K> keySet() {
        if (keySet == null) {
            keySet = new ReferenceKeySet<K, V>(this);
        }
        return keySet;
    }
Returns a set view of this map's keys.

@return a set view of this map's keys