Fixed many various map bugs

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

@@ -5,6 +5,7 @@ import io.anuke.arc.collection.StringMap;
 import io.anuke.arc.files.FileHandle;
 import io.anuke.arc.graphics.Texture;
 import io.anuke.mindustry.Vars;
+import io.anuke.mindustry.game.DefaultWaves;
 import io.anuke.mindustry.game.Rules;
 import io.anuke.mindustry.io.JsonIO;
 
@@ -57,7 +58,9 @@ public class Map implements Comparable<Map>{
 
     /** This creates a new instance.*/
     public Rules rules(){
-        return JsonIO.read(Rules.class, tags.get("rules", "{}"));
+        Rules result = JsonIO.read(Rules.class, tags.get("rules", "{}"));
+        if(result.spawns.isEmpty()) result.spawns = DefaultWaves.get();
+        return result;
     }
 
     /** Whether this map has a core of the enemy 'wave' team. Default: true.