build/transaction.go
func (m AllowTrustBuilder) MutateTransaction(o *TransactionBuilder) error {
	if m.Err != nil {
		return m.Err
	}

	m.O.Body, m.Err = xdr.NewOperationBody(xdr.OperationTypeAllowTrust, m.AT)
	o.TX.Operations = append(o.TX.Operations, m.O)
	return m.Err
}
func (m AllowTrustBuilder) MutateTransaction(o *TransactionBuilder) error {
	if m.Err != nil {
		return m.Err
	}

	m.O.Body, m.Err = xdr.NewOperationBody(xdr.OperationTypeAllowTrust, m.AT)
	o.TX.Operations = append(o.TX.Operations, m.O)
	return m.Err
}
// MutateTransaction for AllowTrustBuilder causes the underylying AllowTrustOp
// to be added to the operation list for the provided transaction