Comprehensive Rule 602.1a-c 602.1a: Select a Z/X under turn player's control that will attack. 602.1b: Select a Z/X or Player that is next to the attacking Z/X and is not under turn player's control that will be attacked. 602.1c: If 602.1a or 602.1b cannot be done, that battle declaration is not correct, and so you cannot declare battle.
So in this case, no you cannot declare an attack without a proper target.
ok, thx for the answer