code: public Long getCas() {
      if (cas == null) {
        try {
          get();
        } catch (InterruptedException e) {
          status = new OperationStatus(false, "Interrupted", StatusCode.INTERRUPTED);
        } catch (ExecutionException e) {
          getLogger().warn("Error getting cas of operation", e);
        }
      }
      if (cas == null && status.isSuccess()) {
        throw new UnsupportedOperationException("This operation doesn't return"
            + "a cas value.");
      }
      return cas;
    }
docs: Get the CAS for this operation.
  
  The interrupted status of the current thread is cleared by this method.
  Inspect the returned OperationStatus to check whether an interruption has taken place.
  
  @throws UnsupportedOperationException If this is for an ASCII protocol
  configured client.
  @return the CAS for this operation or null if unsuccessful.