protected Collection<RM> handleTimer(MessageCollector collector, TaskCoordinator coordinator) {
    return Collections.emptyList();
  }
Handle the the timer tick for this operator and return the results to be propagated to registered operators.
<p>
Defaults to a no-op implementation.

@param collector  the {@link MessageCollector} in the context
@param coordinator  the {@link TaskCoordinator} in the context
@return  results of the timed operation
samza-core/src/main/java/org/apache/samza/operators/impl/OperatorImpl.java