First argument to writable/readable should be optional

[Rich-Harris]

Describe the bug
It's totally valid to create a store without an initial value, but TypeScript complains:

Expected behavior
store = writable() etc should be accepted by TypeScript. I guess value: T here just needs to be value?: T (and similarly for readable)?

svelte/src/runtime/store/index.ts

Line 64 in 086cff2

export function writable<T>(value: T, start: StartStopNotifier<T> = noop): Writable<T> {

Information about your Svelte project:
It's a SvelteKit project using svelte@3.37.0

Severity
Minor — easily worked around with writable(undefined)

[Conduitry]

The types have been updated in 3.38.3 to indicate that the first argument is optional.