Try send a default header

app/action.rb

@@ -23,7 +23,7 @@ module Adamantium
     handle_exception StandardError => :handle_error
 
     config.default_headers = {
-      "Content-Type" => "text/html"
+      "Content-Type" => "application/octet-stream"
     }
 
     def cache(key:, content:)

config.ru

@@ -20,9 +20,9 @@ end
 
 require "adamantium/middleware/header_fix"
 use Adamantium::Middleware::HeaderFix do |headers, env|
-  # if env["REQUEST_METHOD"] == "HEAD"
+  if env["REQUEST_METHOD"] == "HEAD"
     headers['Content-Type'] = "text/html"
-  # end
+  end
 end
 
 run Hanami.app