YARN has a configuration limit to the number of counters that a job can create (to avoid some bad job from DDOS'ing the service).
When running ITBLL, we ran into this limit due to the default configuration rather low at the time. When YARN notices that the counter limit has been exceeded, it nulls out the Counters object obtained by the Job.
Presently in ITBLL, we have a few places where we (reasonably ) assume that the Counters object would be non-null. Can easily fix this with a null-check.