document.rb in roadie-4.0.0

- old
+ new

@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module Roadie
   # The main entry point for Roadie. A document represents a working unit and
   # is built with the input HTML and the configuration options you need.
   #
   # A Document must never be used from two threads at the same time. Reusing
@@ -48,10 +50,10 @@
       @keep_uninlinable_css = true
       @merge_media_queries = true
       @html = html
       @asset_providers = ProviderList.wrap(FilesystemProvider.new)
       @external_asset_providers = ProviderList.empty
-      @css = ""
+      @css = +""
       @mode = :html
     end
 
     # Append additional CSS to the document's internal stylesheet.
     # @param [String] new_css