Amanda Bynes -- All Charges DISMISSED In Bong Case

Amanda Bynes' rap sheet just got a little shorter ... a judge has DISMISSED all charges in connection with her NYC pot bust -- so it's like it never happened.

It's exactly what we said would happen ... if Amanda kept her nose clean for 6 months -- and she has -- she would have the slate wiped clean in her criminal case.

You may remember ... Bynes allegedly tossed a bong out of the window of her NYC apartment ... when cops responded to complaints from neighbors that she was smoking weed and acting erratically.

She was charged with marijuana possession, evidence tampering and reckless endangerment.

Amanda went to court last January and was told if she stayed out of trouble ... the case would go away and that's exactly what happened in court today.