Fixed crash

core/src/io/anuke/mindustry/maps/Sector.java

@@ -27,6 +27,7 @@ public class Sector{
     public int width = 1, height = 1;
     /**Num of missions in this sector that have been completed so far.*/
     public int completedMissions;
+
     /**Display texture. Needs to be disposed.*/
     public transient Texture texture;
     /**Missions of this sector-- what needs to be accomplished to unlock it.*/

core/src/io/anuke/mindustry/maps/missions/Mission.java

@@ -29,7 +29,7 @@ public abstract class Mission{
     }
 
     public GameMode getMode(){
-        return null;
+        return GameMode.noWaves;
     }
 
     /**Sets the message displayed on mission begin. Returns this mission for chaining.*/