I wouldn't exactly call that negative space. Take it from these links what they define it as,
#1,
#2,
#3,
#4. Think my English isn't good enough to convey what I'm trying to express, but negative space adds to the main subject on top off being in it... Here, would I miss the dark background were it replaced by something else? Well no, I wouldn't miss it at all. In fact I rather it be replaced, for I don't get the comparison/contrast between the two variables.
Now the idea of "empty feeling", is the image composed with it in mind or was it derived only after shooting and looking at the image. What is it you are trying to say by composing a flower against an dark background, what is empty about it? Why should an empty feeling exist here? Is it empty based on comparing solid vs darkness, should it have any other deeper meaning besides the physical dimension? Is there an emotional 'thingy' people should be aware of? Could you have used another object to signify what you're trying to say? Could negative space be comprised of something else?
Technical-wise, I'd prefer a softer light instead of the harsh direct currently. This flower (forgot the name) is notoriously hard to capture, thus it usually looks 2D in photographs. Make better use of lighting which wraps and create depth & volume, and also to give it a feminine/delicate appearance which may be better suited for your 'empty feeling' search.
It really looks more like a snapshot at the moment but I've given benefit of doubt since negative space has been brought up. Hopefully a stronger composition involving negative space can be presented in the future. Cheers.
Ps. Hmm ok since the darkness is not the main subject then truly it is
negative space, for the flower being
positive space. However whether you can call it a usage of negative space I have my reservations. Just to make things clearer. Sorry for any confusion. Thanks.