Computed binding between two components throws error: flatten(...) is null

[i80and]

Description

I'm porting a feedback widget to Svelte. The widget has methods to add questions to a list; each question can either be a binary choice or a freeform text box. I want to funnel each question widget's value into an object mapping questionID -> answer in the parent component.

It looks like you can bind <input> element values to a computed attribute (e.g. https://svelte.technology/repl?version=1.22.2&gist=20fa77ffb878bdcc7a0e496df0df8e4f) but you cannot bind nested component state to a computed attribute.

Simple reproduction

https://svelte.technology/repl?version=1.22.2&gist=1aafb1485e848d0da03d647b40d75f28

Backtrace

TypeError: Cannot read property 'name' of null
    at Object.visitBinding [as Binding] (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:13339:40)
    at /Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:13439:35
    at Array.forEach (native)
    at visitComponent (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:13438:10)
    at visitElement (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:14264:16)
    at visit$1 (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:14605:5)
    at /Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:14404:9
    at Array.forEach (native)
    at visitChildren (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:14403:19)
    at getBranches (/Users/andrew/Documents/greni/node_modules/svelte/compiler/svelte.js:14384:5)

[Rich-Harris]

Fixed in 1.22.3 — thanks