Revocation of trust: testamentary trusts are revocable at the testator's pleasure; non testamentary revocation is conditional. Section 78 provides that trusts created by will are revocable at the testator's pleasure; non testamentary trusts are revocable only where all beneficiaries competent to contract consent, where a power of revocation is expressly reserved in a non testamentary instrument or by word of mouth, or where the trust for payment of the author's debts has not been communicated to creditors, in which case the author may revoke.