I'm assuming they need salary filler.
The Nets have three free agents. Andray Blatche, who wants to be a Net and is willing to play for the minimum (because he was amnestied, any salary he gets will just offset what he is getting from his Washington contract, so he wants to make the Wizards pay for it, out of spite). Jerry Stackhouse, who is expected to retire. And Keith Bogans.
I haven't done the math but it could be that Bogans is needed to allow the Nets to keep Reggie Evans. Bogans can be paid more than Toko Shengelia or Tyshawn Taylor.
The CBA requires that Bogans be signed to a three-year deal, but only the first year has to be justified. I expect he will get a non-Bird rights raise over the minimum salary and the Celtics will be expected to waive him if they don't use his salary in a trade.