public static void waitForLastKey() {
    WaitCriterion wc = new WaitCriterion() {
      @Override
      public boolean done() {
        return lastKeyReceived;
      }

      @Override
      public String description() {
        return "Last key NOT received.";
      }
    };
    GeodeAwaitility.await().untilAsserted(wc);
  }
Simulates old value null, entry null
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/DeltaPropagationStatsDUnitTest.java