docs: public final void checkIntegrity() {
      executeWithGlobalLock(new Job<Void>() {
        @Override
        public Void call() {
          IntegrityState is = getIntegrityState();
          if (is.getStateFlags() > 0) {
            throw new Error(
              "cache2k integrity error: " +
              is.getStateDescriptor() + ", " + is.getFailingChecks() + ", " + generateInfoUnderLock(HeapCache.this, clock.millis()).toString());
          }
          return null;
        }
      });
    }