build/transaction.go
func (m Defaults) MutateTransaction(o *TransactionBuilder) error {

	if o.TX.Fee == 0 {
		o.TX.Fee = xdr.Uint32(100 * len(o.TX.Operations))
	}

	if o.NetworkID == [32]byte{} {
		o.NetworkID = DefaultNetwork.ID()
	}
	return nil
}
func (m Defaults) MutateTransaction(o *TransactionBuilder) error {

	if o.TX.Fee == 0 {
		o.TX.Fee = xdr.Uint32(100 * len(o.TX.Operations))
	}

	if o.NetworkID == [32]byte{} {
		o.NetworkID = DefaultNetwork.ID()
	}
	return nil
}
// MutateTransaction for Defaults sets reasonable defaults on the transaction being built