No need to stringify event names (= method names) that always are Symbols

activesupport/lib/active_support/subscriber.rb

@@ -81,7 +81,7 @@ module ActiveSupport
         attr_reader :subscriber, :notifier, :namespace
 
         def add_event_subscriber(event) # :doc:
-          return if invalid_event?(event.to_s)
+          return if invalid_event?(event)
 
           pattern = prepare_pattern(event)
 
@@ -92,7 +92,7 @@ module ActiveSupport
         end
 
         def remove_event_subscriber(event) # :doc:
-          return if invalid_event?(event.to_s)
+          return if invalid_event?(event)
 
           pattern = prepare_pattern(event)
 
@@ -107,7 +107,7 @@ module ActiveSupport
         end
 
         def invalid_event?(event)
-          %w{ start finish }.include?(event.to_s)
+          %i{ start finish }.include?(event.to_sym)
         end
 
         def prepare_pattern(event)