NullPointerException even though mp3 file is in data folder.

I'm trying to get a song to play with Minim, but it's not working because of the error NullPointerException even though the file is in the data folder. I'm using a global variable AudioPlayer player;

Then in setup() I'm loading it with player = minim.loadFile("PiecesofWhat.mp3");

Then following that with player.play();

And draw contains the usual waveform loop that comes with the example code. 

Can anyone help me?

Thank you in advance!