Looks like your error message is coming from the
jekyll-analytics plugin. I tried to build your site and added
--verbose --trace and got this output.
E:/Ruby24-x64/lib/ruby/gems/2.4.0/gems/jekyll-analytics-0.1.6/lib/jekyll-analytics.rb:7:in `inject': undefined method `keys' for nil:NilClass (NoMethodError)
Disabling that plugin in the Gemfile stops the error.
I didn’t dig much deeper into your repo but did notice your
_layouts/default.html is a little screwy. It needs YAML Front Matter so that could potentially bite you later.