Array of Sprite with Andengine

Array of Sprite with Andengine

I'm developing a game for android using Andengine but I have a problem
when I try to create each Sprite.
In my declaration I have
private Sprite[] bolaSprite = new Sprite[16];
and then I get a NullPointerException error trying to initialize the first
Sprite :
bolaSprite[0] = new Sprite(249, 242, resourcesManager.bola_region, vbom);
Can somebody tell me why that's happening ?