@edu.umd.cs.findbugs.annotations.SuppressWarnings(value = "MS_EXPOSE_REP",
      justification = "singleton pattern")
  public static VisibilityLabelsCache get() {
    // By the time this method is called, the singleton instance of VisibilityLabelsCache should
    // have been created.
    if (instance == null) {
      throw new IllegalStateException("VisibilityLabelsCache not yet instantiated");
    }
    return instance;
  }
@return Singleton instance of VisibilityLabelsCache when this is called before calling
        {@link #createAndGet(ZKWatcher, Configuration)}
hbase-server/src/main/java/org/apache/hadoop/hbase/security/visibility/VisibilityLabelsCache.java