Yes of course we can generalise it.
We know that for a dfa comprising of n states and m input alphabets ,
No of DFA possible = n * nnm * 2n assuming that the DFA is a labelled one and hence the choice of start state matters
Now coming to your question , we need to accept an empty language.As we know final states are meant for acceptance only.So if we want that we accept the empty language what we need to do is just we do not choose any of the states as the final state and hence all states will be rejecting states and hence we will get empty language.By empty language we mean nothing is accepted.
So given an initial state there is only 1 way of choosing final state and that is not choosing any of the state as the final state
Hence the 3rd term "2n" in general expression reduces to 1 only.
Hence no of DFA which accepts empty language = n * nnm