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