This commit fixes an issue where an error is thrown if the default value
for a Kudu column is set to NULL.
Change-Id: Ida27ce56f1dd7603485a69c680db3bcea6702aff
Reviewed-on: http://gerrit.cloudera.org:8080/5405
Reviewed-by: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Tested-by: Internal Jenkins