Flaws? Well, for a start there's the fact that it's completely ridiculous...
Any fuel to be used for refueling would have to be launched with the craft - it all has to come from earth anyway so there's no benefit to be gained. It doesn't make any sense, it's just adding in an unnecessary layer of complication.
Even apart from that, a docking at the L2 point in order for the refueling would be a ridiculously complicated process - some kind of automatic system could be designed to do it, but (unless the craft's final destination is the lagrange point, in which case it obviously isn't going to need refueling) that would waste a lot of fuel in order to stop the craft so that it could dock with the tanker.
And the orbit of the craft to be refueled would have to pass through the lagrange point which in almost all cases would waste more fuel than could possibly be gained by the refueling (this is assuming that a transfer orbit through the lagrange point is even possible).