constructor(buffer = Uint8Array.from([2, 0, 0, 0, 0, 0, 0, 0, 0, 0])) {
    this.tx = Transaction.fromBuffer(buffer);
    checkTxEmpty(this.tx);
    Object.defineProperty(this, 'tx', {
      enumerable: false,
      writable: true,
    });
  }
This class implements the Transaction interface from bip174 library.
It contains a bitcoinjs-lib Transaction object.