getPatch() {
    const objectMeta = {_root: {parentObj: null, parentKey: null, opId: null, type: 'map', children: {}}}
    const docState = {blocks: this.blocks, actorIds: this.actorIds, objectMeta, maxOp: 0}
    const diffs = this.initPatch ? this.initPatch : documentPatch(docState)
    return {
      maxOp: this.maxOp, clock: this.clock, deps: this.heads,
      pendingChanges: this.queue.length, diffs
    }
  }
Returns a patch from which we can initialise the current state of the backend.