Incorrect inferred type with allowUndefinedOverrides: false

[tippfelher]

import { merge } from "ts-deepmerge";

const a: { o: string } = { o: "Hello" };

const b: { o?: string } = {};

const c = merge.withOptions({ allowUndefinedOverrides: false }, a, b);

// this is incorrect
//   c is of type { o: string | undefined }
// but should be
//   { o: string }
// since c.o can never be undefined

[voodoocreation]

Hey, this is a duplicate of this issue - unfortunately I wasn't able to get the types to work as you're expecting here, (more details provided in my replies on the other issue), but contributions are always welcome if you'd like to give it a go and open a PR! 🙏