function emptyChange(doc, options) {
  if (doc[OBJECT_ID] !== '_root') {
    throw new TypeError('The first argument to Automerge.emptyChange must be the document root')
  }
  if (typeof options === 'string') {
    options = {message: options}
  }
  if (options !== undefined && !isObject(options)) {
    throw new TypeError('Unsupported type of options')
  }

  const actorId = getActorId(doc)
  if (!actorId) {
    throw new Error('Actor ID must be initialized with setActorId() before making a change')
  }
  return makeChange(doc, new Context(doc, actorId), options)
}
Triggers a new change request on the document `doc` without actually
modifying its data. `options` is an object as described in the documentation
for the `change` function. This function can be useful for acknowledging the
receipt of some message (as it's incorported into the `deps` field of the
change). Returns a two-element array `[doc, request]` where `doc` is the
updated document, and `request` is the change request to send to the backend.