StrictNull check Tuple overflow

[sebdoucet]

TypeScript Version: 2.4.1

Code

const tuple: [string, number] = ["", 0];
const value = tuple[2];

Expected behavior:
Not compiling. You cant define a type based on what is currently define in the array.
This behavior broke the strict null check validation because this value should be undefined or the accessor non legit.

Actual behavior:
Compile and value as the type of all types defined in the tuple, in this case string | number.

[imcotton]

When accessing an element outside the set of known indices, a union type is used instead

from: handbook#tuple

[sebdoucet]

Because it's in the hanbook, that does not make more cense to me.

Why it's not at least a tuple combine with undefined. It broke strict null checking like string | number | undefined

[mhegazy]

Duplicate of #6229

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.