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=== tests/cases/compiler/optionalParameterRetainsNull.ts ===
interface Bar { bar: number; foo: object | null; }
>bar : number
>foo : object | null
>null : null
let a = {
>a : { test<K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined): void; }
>{ test<K extends keyof Bar> (a: K, b?: Bar[K] | null) { }} : { test<K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined): void; }
test<K extends keyof Bar> (a: K, b?: Bar[K] | null) { }
>test : <K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined) => void
>a : K
>b : Bar[K] | null | undefined
>null : null
};
a.test("bar", null); // ok, null is assignable to number | null | undefined
>a.test("bar", null) : void
>a.test : <K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined) => void
>a : { test<K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined): void; }
>test : <K extends "bar" | "foo">(a: K, b?: Bar[K] | null | undefined) => void
>"bar" : "bar"
>null : null
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