Create the class DefaultFireFighter

src/main/java/model/ExtinguishFire/DefaultFireFighter.java

+package model.ExtinguishFire;
+
+public class DefaultFireFighter {
+}

src/main/java/model/ExtinguishFire/FireFighter.java

@@ -3,7 +3,7 @@ package model.ExtinguishFire;
 import model.Board.BoardElement;
 import util.Position;
 
-public class FireFighter extends BoardElement {
+public abstract class FireFighter extends BoardElement {
     public FireFighter(Position position) {
         super(position);
     }