Add NullObject class.

Not sure yet if we’ll end up using this as the cases where I thought
this would apply I was able to just use Array() to achieve the same
result. This is good to have though and would like to start using this
in my own projects too.
Remove bundler_args

The Gemfile installs dalli only in production but since we have a
cache.rb in lib (all files in lib are required) that requires dalli
even though we don’t use the class unless in production. I’ll find a
better way of how to solve this. Perhaps it is just best to use dalli
locally but I’d rather not. I have tried to make everything else that
runs in production run locally so I guess it shouldn’t be any different
with dalli.