[on_and_off]

as stated in another comment, you get : s exception: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Integer.toString()' on a null object reference

the name of the method causing the crash (toString in that sample) + the line number and location thanks to the stacktrace (although in some rare case it is 100% accurate, but still pretty close, maybe that's due to runtime inlining) and it is very trivial to know where the exception comes from.