Remove superfluous return value from 'before' callbacks

app/models/contest.rb

@@ -36,7 +36,6 @@ class Contest < ApplicationRecord
     end
 
     update_contest_scores if finalized_at_was && finalized_at.nil?
-    true
   end
 
   # calculate contest scores again from scratch

app/models/item.rb

@@ -12,7 +12,6 @@ class Item < ApplicationRecord
 
   before_create do
     self.scan_token = SecureRandom.random_number(100000000)
-    true
   end
 
   def scan_token

app/models/submission.rb

@@ -33,7 +33,6 @@ def user_problem_relation
     end
     self.evaluation = points.nil? || maximum_points.nil? ? nil : (points / maximum_points).to_f
     update_test_messages
-    true
   end
 
   before_create do

app/models/user.rb

@@ -18,7 +18,6 @@ class User < ApplicationRecord
 
   before_save do
     self.can_change_username = false if username_changed? # can only change username once
-    true # this line should be removed once we upgrade to Rails >= 5.1, see https://guides.rubyonrails.org/5_1_release_notes.html#active-model-removals
   end
 
   has_many :problems

config/initializers/new_framework_defaults.rb

@@ -22,4 +22,4 @@
 Rails.application.config.active_record.belongs_to_required_by_default = false
 
 # Do not halt callback chains when a callback returns false. Previous versions had true.
-ActiveSupport.halt_callback_chains_on_return_false = true
+ActiveSupport.halt_callback_chains_on_return_false = false