code: func (c *BoundContract) Transfer(opts *TransactOpts) (tx *Transaction, _ error) {
  	rawTx, err := c.contract.Transfer(&opts.opts)
  	if err != nil {
  		return nil, err
  	}
  	return &Transaction{rawTx}, nil
  }
docs: // Transfer initiates a plain transaction to move funds to the contract, calling
  // its default method if one is available.