@Override
  public ScheduledFunction getScheduledFn() {
    FoldLeftFunction fn = window.getFoldLeftFunction();
    return fn instanceof ScheduledFunction ? (ScheduledFunction) fn : null;
  }
Get the default triggering interval for this {@link WindowOperatorSpec}

This is defined as the GCD of all triggering intervals across all {@link TimeBasedTrigger}s configured for
this {@link WindowOperatorSpec}.

@return the default triggering interval
samza-core/src/main/java/org/apache/samza/operators/spec/WindowOperatorSpec.java