Spread '...' should throw TypeError for 'undefined'

[DLehenbauer]

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

Code

const a = [];
const x: number[] | undefined = undefined;

a.push(...x);

Expected behavior:
Always throws 'TypeError: x is not iterable', regardless of the '--target'.

Actual behavior:
For '--target es5', no error is thrown. This is because the spread is transformed into a call to '.apply()', which accepts 'undefined'.

(I stumbled on this when compiling tsc with '--target es2015', which revealed that the compiler had a minor dependency on the noncompliant spread behavior.)

[mhegazy]

Seems to be the same issue as #1679

[DLehenbauer]

You're right, it's a dupe. (Sorry, I didn't include closed issues in my search.)

[mhegazy]

thanks. closing.