Advanced probability and applications

You play a game where you have to choose between 3 doors (say A,B,C): behind one of these doors, there is a treasure, behind the other two, nothing. You choose a door, say A. Then a genie comes and opens another door, say B, showing you that there is nothing behind this door. The genie then tells you that you are allowed to change your mind and choose door C if you prefer. Will you change your mind? (whatever your answer is, you are also welcome to post an argument justifying your decision in the forum)