block-justifications.js

const { ApiPromise, WsProvider } = require("@polkadot/api");

async function main() {
  const provider = new WsProvider('wss://kusama-rpc.polkadot.io');
  const api = await ApiPromise.create({ provider });
  const number = 10857954;
  const hash = await api.rpc.chain.getBlockHash(number);
  const block = await api.rpc.chain.getBlock.raw(hash); // same with chain.getBlock(hash);

  console.log(block.justifications); // result is null
}

main().catch(e => console.log(e));