code: public Session getSession(String key) {
          sessionsLockRead.lock();
          try {
              SessionEntry entry = this.sessions.get(key);
              return entry != null ? entry.getSession() : null;
          } finally {
              sessionsLockRead.unlock();
          }
      }
docs: Returns the {@link Session} stored under the given {@code key} or {@code null} if there is no such session.
  
  @param key the key to look for
  @return the {@link Session} stored under the given {@code key} or {@code null} if there is no such session.