anchor.diff:      if (!_nodes.contains(node)) {
         return;
       }
  -    _httpPool.leave(node._httpEndpoint);
  -    _pbPool.leave(node._pbEndpoint);
  +    if (node._httpEndpoint != null) {
  +      _httpPool.leave(node._httpEndpoint);
  +    }
  +    if (node._pbEndpoint != null) {
  +      _pbPool.leave(node._pbEndpoint);
  +    }
       _nodes.remove(node);
     }
   
  
positive.code:   Endpoint _pbEndpoint;
  
    Node(this.host, {this.httpPort: 8098, this.pbPort: 8087}) {
      _httpEndpoint = new Endpoint(host, httpPort);
      _pbEndpoint = new Endpoint(host, pbPort);
    }
  
    bool operator ==(Node other) =>
  
negative.code:     if (_nodes.contains(node)) {
        return;
      }
      if (node._httpEndpoint != null) {
        _httpPool.join(node._httpEndpoint);
      }
      if (node._pbEndpoint != null) {
        _pbPool.join(node._pbEndpoint);
      }
      _nodes.add(node);
    }
  
  