function TransactionMessage(arg, options) {
  Message.call(this, options);
  this.command = 'tx';
  this.Transaction = options.Transaction;
  $.checkArgument(
    _.isUndefined(arg) || arg instanceof this.Transaction,
    'An instance of Transaction or undefined is expected'
  );
  this.transaction = arg;
  if (!this.transaction) {
    this.transaction = new this.Transaction();
  }
}
@param {Transaction=} arg - An instance of Transaction
@param {Object} options
@extends Message
@constructor