Problem 4a: `Autobase.append` "Cannot read property 'length' of undefined"

[r-token]

When calling Autobase.append, I receive an error that says "TypeError: Cannot read property 'length' of undefined".

Here's the full stack trace:

/path-to-project/node_modules/autobase/index.js:441
    const head = await this._getInputNode(input, input.length - 1)
                                                       ^

TypeError: Cannot read property 'length' of undefined
    at Autobase.append (/path-to-project/node_modules/autobase/index.js:441:56)
    at async file:///path-to-project/autobase-practice.js:17:1

Here's my code:

import Corestore from 'corestore'
import Autobase from 'autobase'
import ram from 'random-access-memory'

// Create two chat users, each with their own Hypercores.
// Here since we'll be rerunning the same code a lot, we'll use the ram storage

const store = new Corestore(ram)
const userA = store.get({ name: 'userA' })
const userB = store.get({ name: 'userB' })

// Make an Autobase with those two users as inputs.

const baseA = new Autobase([userA, userB], { input: userA })
const baseB = new Autobase([userA, userB], { input: userB })

await baseA.append('A0: hello!')
await baseB.append('B0: hi! good to hear from you')
await baseA.append('A1: likewise. fun exercise huh?')
await baseB.append('B1: yep. great time.')

// Let's print all messages in causal order
for await (const node of baseA.createCausalStream()) {
  console.log(node.value.toString())
}

And here's my package.json:

{
  "name": "autobase-practice",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "type": "module",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "autobase": "^1.0.0-alpha.8",
    "chalk": "^5.0.0",
    "corestore": "^6.0.1-alpha.9",
    "random-access-memory": "^4.0.0"
  }
}