There's a bit of explanations:

This frame isn't an a actual in-game void. That's just an a testing frame, but I wanted to use it as void. But after we had some chapters change, this frame is now just an a testing.

And no, there's NO Gaster in this frame. Firstly there was Gaster, but, again, after some changes in chapters and characters, we had to delete Gaster from this frame.