@Override
  public void handshake() {
    throw new UnsupportedOperationException(PLACEHOLDER_ERROR_MSG);
  }
This class is a placeholder and should not be initialized. It represents the all the IoTDB pipe
connectors that can not be implemented in the node-commons module. Each IoTDB pipe connector has
a real implementation in the server module but cannot be imported here. The pipe agent in the
server module will replace this class with the real implementation when initializing the IoTDB
pipe connector.
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/pipe/agent/plugin/builtin/connector/PlaceholderConnector.java