The return type of the produce method will have an additional undefined

🙋‍♂ Question

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import { produce } from 'immer';

const func = produce((state: Record<string, string> = {}): Record<string, string> => {
  return state;
});

In the above code, I expect the type of the func to be Record<string, string>, but the actual type check returns Record<string, string> | undefined, how can I avoid the undefined?

This problem only occurs in 9.x versions

Link to repro

https://codesandbox.io/s/immer-sandbox-forked-n1okz2?file=/src/index.ts

Environment

We only accept questions against the latest Immer version.

• Immer version:
• Occurs with setUseProxies(true)
• Occurs with setUseProxies(false) (ES5 only)

Start with the TypeScript example in the linked CodeSandbox, especially src/index.ts and its produce call, and reproduce the reported inferred return type. Compare the behavior with the stated expectation for the 9.x versions. Done means the example's type check no longer adds undefined to the returned Record type.