fix AI bug

battleship/ai.py

@@ -60,7 +60,9 @@ class AIPlayer(Player):
     def guess(self, opponent: Player) -> Coordinate:
         for guess in self.guesses:
             if self.coord_status(guess, opponent) == CoordStatus.HIT:
-                return self.guess_near(guess, opponent)
+                candidate = self.guess_near(guess, opponent)
+                if candidate:
+                    return candidate
 
         while True:
             guess = random.choice(opponent.board.columns), random.choice(opponent.board.rows)