style: if ! changed by unless

- if ! changed by unless as it is more readable
- !object.blank? is equivalent to object.present?, also more readable

app/controllers/admin/events_controller.rb

@@ -103,7 +103,7 @@ module Admin
       comment.commentable = @event
       comment.user_id = current_user.id
       comment.save!
-      if !params[:parent].nil?
+      unless params[:parent].nil?
         comment.move_to_child_of(params[:parent])
       end
 
@@ -202,7 +202,7 @@ module Admin
 
     def get_event
       @event = @conference.program.events.find(params[:id])
-      if !@event
+      unless @event
         redirect_to admin_conference_program_events_path(conference_id: @conference.short_title),
                     error: 'Error! Could not find event!'
         return

app/controllers/admin/questions_controller.rb

@@ -67,7 +67,7 @@ module Admin
     def destroy
       if can? :destroy, @question
         # Do not delete global questions
-        if !@question.global
+        unless @question.global
 
           # Delete question and its answers
           begin

app/controllers/application_controller.rb

@@ -47,7 +47,7 @@ class ApplicationController < ActionController::Base
   rescue_from CanCan::AccessDenied do |exception|
     Rails.logger.debug "Access denied on #{exception.action} #{exception.subject.inspect}"
     message = exception.message
-    message << ' Maybe you need to sign in?' if !current_user
+    message << ' Maybe you need to sign in?' unless current_user
     redirect_to root_path, alert: message
   end
 

app/controllers/conference_registrations_controller.rb

@@ -52,7 +52,7 @@ class ConferenceRegistrationsController < ApplicationController
       ahoy.track 'Registered', title: 'New registration'
 
       # Sign in the new user
-      if !current_user
+      unless current_user
         sign_in(@registration.user)
       end
 
@@ -96,7 +96,7 @@ class ConferenceRegistrationsController < ApplicationController
 
   def set_registration
     @registration = Registration.find_by(conference: @conference, user: current_user)
-    if !@registration
+    unless @registration
       redirect_to new_conference_conference_registration_path(@conference.short_title),
                   error: "Can't find a registration for #{@conference.title} for you. Please register."
     end