For for InMemoryTicketComponent, which iterates over the keys in the cache

- The root issue is that some entries are null markers
 - Cache entries could disappear during the iteration anyway
 - Cleaned up some comments in the cache code


git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@17073 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/security/authentication/InMemoryTicketComponentImpl.java

@@ -229,6 +229,11 @@ public class InMemoryTicketComponentImpl implements TicketComponent
         for (String key : ticketsCache.getKeys())
         {
             Ticket ticket = ticketsCache.get(key);
+            // Hack: The getKeys() call might return keys for null marker objects, yielding null values
+            if (ticket == null)
+            {
+                continue;
+            }
             if (ticket.getUserName().equals(userName))
             {
                 toRemove.add(ticket.getTicketId());