Replace None with UNSET_VALUE for Cassandra query padding
Replace None with UNSET_VALUE for Cassandra query padding

Fixes #180

criteo/biggraphite,iksaif/biggraphite,criteo/biggraphite,Thib17/biggraphite,Thib17/biggraphite,iksaif/biggraphite,Thib17/biggraphite,criteo/biggraphite,Thib17/biggraphite,criteo/biggraphite,iksaif/biggraphite,dpanth3r/biggraphite,iksaif/biggraphite