[Bug]: Documented "Loops: Chatbot" example doesn't work

### What happened?

[In the documented example](https://rivet.ironcladapp.com/docs/user-guide/loops#chatbot), the loop controller doesn't receive a default value for "message history".

I could only get the example to work by adding an empty array node to the default for data 1, so it gets seeded with `[]` rather than `undefined`.

### What was the expected functionality?

Documented example doesn't work

### Relevant screenshots

Fixed example:


Open the documented Loops: Chatbot example at the linked documentation URL and inspect how the loop controller initializes message history, especially data 1. Confirm the example works when message history is seeded with an empty array, as shown in the reported fixed example.

Written by the indexing model from the issue text.