render :json => nil

render :json => nil causes render to ignore :json

in actionpack/lib/action_controller/base.rb line 954 evaluates to false - this ends up failing out with a could not find method.erb error

 954           elsif json = options[:json]
 955             json = json.to_json unless json.is_a?(String)
 956             json = "#{options[:callback]}(#{json})" unless options[:callback].blank?
 957             response.content_type ||= Mime::JSON
 958             render_for_text(json, options[:status])
 959 
 960           elsif options[:partial]

attached a test which fails