Well yes, the absence of something can be considered something in its own right. There's probably a more eloquent way to put that but it escapes me at the moment.
There was a philosopher (Sartre?) who was to meet his friend at a cafe in Paris. His friend was late, and as the philosopher sat drinking coffee and waiting, he realized that his friend's absence was present, and this this absence was different from the absence of all the other people who also weren't at the cafe.