Hard Brake Pedal '02 I35

[JLATL63]

Hey, new to the forum. Does anyone know if the brake booster vacuum line on a 2002 I35 has a built in check valve? The section the attaches to the engine manifold has a flare to it that looks like a valve. My car experiences a hard brake pedal if I have to suddenly stop while accelerating from idle. Otherwise it performs perfectly. I was hoping that the sudden drop in manifold vacuum when pulling off the gas was making the boost drop off. Had some close calls of late and the wife won't drive my I35 ;-)