That would be $0 - and plenty of kets. People are missing the point here. I don't actually care much about the notation. I care that the algorithms are basically constructed out of matrix math. If you construct classical algorithms that way, you will find that aside from things like Fourier transforms (coincidence?), there's not much you can represent. The presence of a single ket basically undermines the idea that you don't need to do matrix math for quantum computing.