no fallar si el intervalo está vacío

app/controllers/stats_controller.rb

@@ -137,7 +137,7 @@ class StatsController < ApplicationController
   # @return [Symbol]
   def interval
     @interval ||= begin
-      i = params[:interval].to_sym
+      i = params[:interval]&.to_sym
       Stat::INTERVALS.include?(i) ? i : :day
     end
   end

app/views/stats/index.haml

@@ -10,7 +10,7 @@
 
     .mb-3
       - Stat::INTERVALS.each do |interval|
-        = link_to t(".#{interval}"), site_stats_path(interval: interval, urls: params[:urls]), class: "btn #{'btn-primary active' if params[:interval].to_sym == interval}"
+        = link_to t(".#{interval}"), site_stats_path(interval: interval, urls: params[:urls]), class: "btn #{'btn-primary active' if @interval == interval}"
 
     .mb-3
       %h2= t('.host.title', count: @hostnames.size)