LUPITA NYONG'O DRESS THIEF GETS AWAY WITH IT ... Calvin Klein drops case.

The guy who burglarized Lupita Nyong'o's hotel room and stole what he THOUGHT was a $150,000 dress has gotten away with the crime, because Calvin Klein wants the whole thing to go away.

According to TMZ law enforcement sources say reps from Calvin Klein contacted the L.A. County Sheriff's Dept. earlier this week and said they had no interest in pursuing the case now that they got the dress back ...and it's pretty obvious why.

The thief called TMZ Friday and indignantly said he took 2 of the pearls down to the L.A. Garment District for appraisal, only to learn they were fake and worthless. He told us he had returned the dress to The London West Hollywood hotel and left it under a sink in a 2nd floor bathroom. We told the cops, and they got the dress.