Initialize config.assets.version the same way it's done in Sprockets

actionpack/lib/sprockets/railtie.rb

@@ -20,7 +20,7 @@ class Railtie < ::Rails::Railtie
       app.assets = Sprockets::Environment.new(app.root.to_s) do |env|
         env.static_root = File.join(app.root.join('public'), config.assets.prefix)
         env.logger = ::Rails.logger
-        env.version = ::Rails.env + '-' + config.assets.version
+        env.version = ::Rails.env + "#{'-' + config.assets.version if config.assets.version.present?}"
 
         if config.assets.cache_store != false
           env.cache = ActiveSupport::Cache.lookup_store(config.assets.cache_store) || ::Rails.cache

railties/lib/rails/application/configuration.rb

@@ -37,6 +37,7 @@ def initialize(*)
         @assets.paths      = []
         @assets.precompile = [ /\w+\.(?!js|css).+/, /application.(css|js)$/ ]
         @assets.prefix     = "/assets"
+        @assets.version    = ''
 
         @assets.cache_store    = [ :file_store, "#{root}/tmp/cache/assets/" ]
         @assets.js_compressor  = nil