Why is usage optional?

[MatanYadaev]

Describe the bug

openai-node/src/resources/chat/completions.ts

Lines 76 to 79 in abb0be7

	/**
	* Usage statistics for the completion request.
	*/
	usage?: CompletionsAPI.CompletionUsage;

To Reproduce

const chatCompletion = new OpenAI({ ... }).chat.completion.create({ ... })

const totalTokens = chatCompletion.usage.total_tokens; // TS18048: `chatCompletion.usage` is possibly `undefined` 

Code snippets

Library version

v4.31.0

[rattrayalex]

When streaming, this is not supplied from the server currently.

[MatanYadaev]

@rattrayalex Worth mentioning that in the JSDoc of this property. I thought it's optional only when streaming, but wasn't sure if in the other cases, it will 100% be present.

[rattrayalex]

That's a good point, I'll bump that to the relevant team (this would flow through from the OpenAPI spec).

[rattrayalex]

Related: #506