code: func (p *Plugin) PutIfNotExists(key string, value []byte) (succeeded bool, err error) {
  	if p.connection != nil {
  		return p.connection.PutIfNotExists(key, value)
  	}
  	return false, fmt.Errorf("connection is not established")
  }
docs: // PutIfNotExists puts given key-value pair into etcd if there is no value set for the key. If the put was successful
  // succeeded is true. If the key already exists succeeded is false and the value for the key is untouched.