docs: public void connectionClosed() {
          lock.lock();
          try {
              log.info("Server channel closed.");
              connectionOpen = false;
  
              try {
                  if (state != null && state.getContract() != null) {
                      StoredPaymentChannelServerStates channels = (StoredPaymentChannelServerStates)
                              wallet.getExtensions().get(StoredPaymentChannelServerStates.EXTENSION_ID);
                      if (channels != null) {
                          StoredServerChannel storedServerChannel = channels.getChannel(state.getContract().getTxId());
                          if (storedServerChannel != null) {
                              storedServerChannel.clearConnectedHandler();
                          }
                      }
                  }
              } catch (IllegalStateException e) {
                  // Expected when we call getContract() sometimes
              }
          } finally {
              lock.unlock();
          }
      }