DDF-169 Implement null checks and fix generic Exception

Also adds tests
Merge pull request #1 from bradh/master

DDF-169 Implement null checks and fix generic Exception
Reviewed by: @mrmateo
Merge pull request #2 from bradh/DDF-456

[DDF-456] Switch to slf4j
Reviewed by: @mrmateo and @shaundmorris
DDF-458: Updated to build on JDK7 and JDK8.
[DDF-456] Switch from java.util.logging to slf4j