I've noticed a warning during our test suite with JRuby (9.3.1.0, 9.3.8.0), so I'm reporting it here:

/Users/thbar/.rbenv/versions/jruby-9.3.1.0/lib/ruby/gems/shared/gems/rollbar-3.3.1/lib/rollbar/json.rb:8: 
warning: attribute accessor as module_function

I do not know yet why it appears only with JRuby (a good part of the test suite is also compatible with MRI 2.7.x), nor if it is problematic at this point.