Error with strictNullChecks when destructuring.

[rbuckton]

Given the following TypeScript:

const a: { x?: number; } = { };
let x = 0;
({ x = 1 } = a); // error: Type 'number | undefined' is not assignable to 'number'.

However, the destructuring assignment has a default value assigned. This should be treated the same way that strict null checking treats VariableDeclarationList, which does not have this error:

const a: { x?: number; } = { };
let { x = 1 } = a; 
let y: number = x; // ok, x has type 'number'

TypeScript Version:
nightly