Unnecessary uniqueness & force mapping has been removed at BacktraceCleaner#add_gem_filters

railties/lib/rails/backtrace_cleaner.rb

@@ -19,7 +19,7 @@ def initialize
       def add_gem_filters
         return unless defined?(Gem)
 
-        gems_paths = (Gem.path + [Gem.default_dir]).uniq.map!{ |p| Regexp.escape(p) }
+        gems_paths = (Gem.path | [Gem.default_dir]).map { |p| Regexp.escape(p) }
         return if gems_paths.empty?
 
         gems_regexp = %r{(#{gems_paths.join('|')})/gems/([^/]+)-([\w.]+)/(.*)}