//vv Doesn't freak out vv
//...
for (BakedQuad bakedQuad : quads) {
    if(bakedQuad.getFace() == side) {
        faceQuads.add(bakedQuad);
    }
}
//... return faceQuads;

//vv Freaks out vv
//...
for (BakedQuad bakedQuad : quads) {
    if(bakedQuad.getFace() == side) {
        faceQuads.add(bakedQuad);
        faceQuads.add(bakedQuad);
    }
}
//... return faceQuads;