upgrade.rb in httpx-0.13.2

- old
+ new

@@ -31,10 +31,11 @@
 
       module InstanceMethods
         def fetch_response(request, connections, options)
           response = super
 
-          if response && response.headers.key?("upgrade")
+          if response
+            return response unless response.respond_to?(:headers) && response.headers.key?("upgrade")
 
             upgrade_protocol = response.headers["upgrade"].split(/ *, */).first
 
             return response unless upgrade_protocol && options.upgrade_handlers.registry.key?(upgrade_protocol)
 