code: protected List<Entry> getList (Name username)
      {
          if (username instanceof KeepNoHistory) {
              return null;
          }
          List<Entry> history = _histories.get(username);
          if (history == null) {
              _histories.put(username, history = Lists.newArrayList());
          }
          return history;
      }
docs: Returns this user's chat history, creating one if necessary. If the given name implements
  {@link KeepNoHistory}, null is returned.