docs: public static TraceEventBatch log(Category cat) {
          final VoltTrace tracer = s_tracer;
          if (tracer != null && tracer.isCategoryEnabled(cat)) {
              final TraceEventBatch batch = new TraceEventBatch(cat);
              tracer.queueEvent(batch);
              return batch;
          } else {
              return null;
          }
      }