[GSS](7.2.z) Racecondition in RemotingEJBDiscoveryProvider is causing a NullPointerException

A race condition in RemotingEJBDiscoveryProvider is causing a NullPointerException in line 126 during autoboxing the Long value.

This can happen in the case that Thread A is executing line 123 with the containsKey and a return value of true, then Thread B is removing that entry from the Map, while Thread A is calling get in line 126, which will result in a return value of null, leading to a NullPointerException during autoboxing, see:

122     private boolean haveNotExpiredFailedDestination(URI uri) {
123         if(!failedDestinations.containsKey(uri))
124             return false;
125         else {
126             long failureTimestamp = failedDestinations.get(uri);
127             long delta = System.nanoTime() - failureTimestamp;
128             return delta < DESTINATION_RECHECK_INTERVAL;
129         }
130     }