Assuming for a second, this is a serious post.... (which I have no idea of anymore)
How precisely, would you build a craft that had a mass of zero, that somehow manages to conform to the laws of nature?
The mass of the craft doesn't need to be zero when it's built. You're asking us to explain technology that seems to be centuries ahead of our own which is silly. Clearly the craft has technology beyond our understanding, it appears to be breaking physical laws but it most likely isn't, we just don't understand the methods it's using to manoeuvre.