Add null safety to SendDataFromClient/ServerPayload constructors

[EvanHsieh0415]

Description

Add null safety to SendDataFromClient/ServerPayload constructors to fix a codec error.

Example Script

server side:

ItemEvents.rightClicked((event) => {
  event.player.sendData("kubejs:hello_world", { message: "Hello, World!" });
  event.player.sendData("kubejs:hello_world"); // It should no longer cause the error
});

client side:

NetworkEvents.dataReceived('kubejs:hello_world', (event) => {
  if (event.data.message) {
    event.player.tell(event.data.message);
  } else {
    event.player.tell('!!!Hello, World!!!');
  }
});

Other details