Arguably this would be better because if spread was called in a different context (via bind, call, apply, or by placing it on an object) one might WANT this to point to the context. With null, there is no way to set the context of func from outside.

I just think that the question doesn't care about strict or non-strict mode.So,let's assume the function is in non-strict mode ,then null and this are equal 'cause they all point to global object (non-strict mode). And the null is just cool !