Clustering: Error - cannot concatenate 'str' and 'NoneType' objects

I tried 3 - node cluster set up against odl-helium-stable. The integration tests fail mainly with error " TypeError: cannot concatenate 'str' and 'NoneType' objects ". Attached are the reports after integrations tests.

Versions Used:-

OpendayLight Helium Stable - https://jenkins.opendaylight.org/integration/job/integration-helium-project-centralized-integration/lastSuccessfulBuild/artifact/distributions/extra/karaf/target/distribution-karaf-0.2.1-SNAPSHOT.zip

Integration – Latest Integration code - git clone https://git.opendaylight.org/gerrit/p/integration.git

Commands :-

python deploy.py --distribution=distribution-karaf-0.2.1-SNAPSHOT.zip --rootdir=/home/ubuntu --hosts=10.18.161.83,10.18.161.84,10.18.161.85 --user=XXX --password=XXX

pybot -v LEADER:10.18.161.83 -v PORT:8181 -v FOLLOWER1:10.18.161.84 -v FOLLOWER2:10.18.161.85 /home/mininet/integration/test/csit/suites/clustering/

Regards,
Sai Marapareddy