Fixed issue throwing a null exception when a config directory is null.
Fixed issue throwing a null exception when a config directory is
null.

Signed-off-by: Chris Larsen <83037b211e1d109d6858769a113e269c3139ffd3@yahoo-inc.com>

alienth/opentsdb,andyflury/opentsdb,alienth/opentsdb,eswdd/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,ShefronYudy/opentsdb,OpenTSDB/opentsdb,OpenTSDB/opentsdb,ShefronYudy/opentsdb,andyflury/opentsdb,MadDogTechnology/opentsdb,eswdd/opentsdb