Thanks a lot,
in fact you were right
My code output " \n" instead of ā15 10\nā
And the space followed by new line \n trigger this error.
Add a trim like this would remove the error I hope. But it was clearly user mistake (mine). 
String ans = outputs.get(0).trim();
Thanks a lot for details of score by the way, combo mechanism and points remover are exactly what I needed to understand, I can now safely plunge in A* best path thanks to you!