anchor.diff:  [#negative-cache]
   == Negative caching and nulls
   
  -Sometimes one wants to cache the results of an (expensive) remote call.
  +Sometimes one wants to cache the result of an (expensive) remote call.
   If the remote call fails, one may not want to cache the result or exception,
   but rather re-try the remote call on the next invocation.
   
  
positive.code: ----
      public void caller(int val) {
  
          Integer result = callRemote(val);  //<1>
          if (result != null) {
              System.out.println("Result is " + result);
          else {
             System.out.println("Got an exception");
          }
      }
  
  
negative.code: When the call to the remote throws an exception, the cache does not store the result,
  so that a subsequent call to `callRemote()` with the same parameter value will not be
  answered out of the cache.
  It will instead result in another attempt to call the remote.
  