Fixed #11958

core/src/mindustry/io/TypeIO.java

@@ -147,7 +147,7 @@ public class TypeIO{
         }else if(object instanceof UnitCommand command){
             write.b(23);
             write.s(command.id);
-        }else if(object instanceof Bullet b){ //write bullets as null
+        }else if(object instanceof Bullet b || object instanceof Seq<?> s){ //write bullets as null
             write.b((byte)0);
         }else{
             throw new IllegalArgumentException("Unknown object type: " + object.getClass());