Fix issue in HttpSerializer.formatError where exceptions with null "message" fields (NullPointerException) were throwing another NPE
Fix issue in HttpSerializer.formatError where exceptions with null "message"
fields (NullPointerException) were throwing another NPE

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

alienth/opentsdb,johann8384/opentsdb,ShefronYudy/opentsdb,MadDogTechnology/opentsdb,alienth/opentsdb,eswdd/opentsdb,OpenTSDB/opentsdb,ShefronYudy/opentsdb,OpenTSDB/opentsdb,MadDogTechnology/opentsdb,johann8384/opentsdb,OpenTSDB/opentsdb,andyflury/opentsdb,MadDogTechnology/opentsdb,andyflury/opentsdb,eswdd/opentsdb