Malformed documents and the hasher

[mattcollier]

https://github.com/digitalbazaar/bedrock-ledger-node/blob/master/lib/index.js#L580

A malformed document can result in jsonld.canonize producing an empty string. niUri.digest has no problem hashing an empty string.

What would be desirable behavior for the hasher API when this occurs? Seems to me that there is no valid use case for hashing an empty string, so that should return an error.

This document is invalid because id is not a URL

{
  "@context": [
    "https://w3id.org/webledger/v1",
    "https://w3id.org/security/v1"
  ],
  "id": "07179fd9-4856-4e55-baf8-b2589a037566",
  "type": "WebLedgerEventBlock",
  "blockHeight": 1,
  "previousBlock": "deaffbb3-8e79-4faa-b837-ab833567150b",
  "previousBlockHash": "cc961a7b-513c-4bcc-876c-2fe488162684"
}