TypeScript Version: 2.1.1 / nightly (2.2.0-dev.201xxxxx)

Code

interface Input {
  text?: string;
}

const test = (input: Input): string => {
  return "";
};

test("test");

Expected behavior:
Type mismatch indicated.
It works if I make the Input Interface text member non-optional.
Actual behavior:
No type mismatch indicated.
It works if I make the Input Interface text member non-optional.