Closed

Description
TypeScript Version: 2.9.0-dev.20180412
Code
function assign<T extends object>(to: T, from: T | undefined) {
for (const p in from!)
to[p] = from![p];
return to;
}
Expected behavior:
No error.
Actual behavior:
src/a.ts(3,9): error TS2536: Type 'keyof NonNullable<T>' cannot be used to index type 'T'.
Related issues: #19461