Nicki Minaj -- I Didn't Block Birdman From Party ... Staying Neutral in Lil Wayne Beef

Nicki Minaj did NOT diss her boss Birdman by taking sides in his battle with Lil Wayne -- TMZ has learned the Cash Money CEO's denial from her pre-Grammy party was just a case of bad timing.

Sources close to Minaj tell us ... Birdman was only denied from 1OAK nightclub because the mogul's posse was looking to order bottle service, and the club was closing in 15 minutes.

On top of that, we're told Nicki had already left and the houselights were on in the club.

Sources tell us Nicki -- as well as Drake -- have made a point to stay out of the ongoing legal beef between Weezy and Baby ... even though Wayne says he's taking them with him when he leaves Cash Money.

We're told Nicki and Drake are hoping their bosses can squash this before it gets too messy -- though that ship seems to have sailed long ago.