Bug 445122 - ClassCastException received when
System.getProperties().store() runs on 4.4.1

 - Use an internal string to represent null configuration

Change-Id: I1d2807317cc85510ee1640f6434159b07680586e
Also-By: Thomas Watson <tjwatson@us.ibm.com>
Signed-off-by: Thomas Watson <tjwatson@us.ibm.com>
Signed-off-by: Markus Keller <markus_keller@ch.ibm.com>