build/transaction_envelope.go
func (b *TransactionEnvelopeBuilder) Mutate(muts ...TransactionEnvelopeMutator) {
	b.Init()

	for _, m := range muts {
		err := m.MutateTransactionEnvelope(b)
		if err != nil {
			b.Err = err
			return
		}
	}
}
func (b *TransactionEnvelopeBuilder) Mutate(muts ...TransactionEnvelopeMutator) {
	b.Init()

	for _, m := range muts {
		err := m.MutateTransactionEnvelope(b)
		if err != nil {
			b.Err = err
			return
		}
	}
}
// Mutate applies the provided TransactionEnvelopeMutators to this builder's
// envelope