Off-tapioca, I know, but I'd refute that.
The mechanisms behind gravity are, as yet, undefined, but the current thinking is that it acts through an as-yet-undiscovered "graviton" particle (a boson with zero rest mass and a spin of 2, in order that it acts over long distances, doesn't transfer any energy/motion to an object it strikes in the direction of its travel and comes in limitless numbers). Without anything for the particle to be transferred to - or through - one cannot assume that the particle is transferred at all. As we know, anything that has mass in our universe has gravity. This directly infers, with the above theory, that there is exchange of information between bodies with mass through exchange of gravitons. No transfer = no exchange = no gravity.
We can state what would happen if another object was inserted into the one-body-universe system, but then gravitons would have something to be transferred to and so gravity would exist.
*goes for a lie down*
The comparison is sound though - as it would be with any other force or immutable postulate. Although it may or may not exist individually in a completely closed system, as soon as an attempt is made to detect or define its existence it does exist, as it has something to act upon.
I apologise for this post as, though it seems to make sense at the moment, I am exceedingly drunk and it may transpire that I've just typed complete gobbledegook.