Return both empty and null properties as empty ones in several places

[follis]

With JobOperator you pass a Properties object when submitting a job. The distinction here is what if you pass a null? Or what if you new up a Properties object but don't put any Properties in it? What does JobContext.getJobParameters return? If you have no JobProperties and call JobContext.getJobProperties what do you get back? null or empty? Spec should say...and be consistent