If I understand this correctly than purpose of this method is to add extra attributes to the JSON. `System#as_json` calls super so you should be able to use `as_json` without problem.
```ruby
def as_json(options)
  extra_attributes = [:href, :facts, :idCert, :owner, :autoheal, :release, :releaseVer, :checkin_time, :installedProducts]
  super(if options 
          (options[:methods] ||= []) += extra_attributes 
          # or
          # options[:methods] ||= [] 
          # options[:methods] += extra_attributes  
        else
          { :methods => extra_attributes }
        end)
end
```