Redmine

I have tried to install the Redmine SAML: https://github.com/AlphaNodes/redmine_saml

Has anyone encounter a problem that keep saying: uninitialized constant additional
I have check the init.rb and see that the Additionals is what causing it, but I don't see how it is causing a problem,
I am not a ruby programmer so I am unsure how it is causing problem.

I did look at https://www.redmine.org/boards/3/topics/57005 but no related information that can help me fix this issue.