Form replay on ApacheMP2 causes server error when response body is empty

Affected version

Version: 2.18.2

Platform: Apache

Summary

My application behaves in a slightly unusual, but still legitimate fashion:

• Form is displayed on /
• Form is posted to /login
• After post to /login, session is created and user is redirected to /
• After landing on /, user is redirected to /some/deep/page

This means I have to configure form replay to trigger on /

But when returning to / after logging in (with a valid cookie), the application redirects me with a 302 response without a body, and form replay crashes the request:

Possible fixes

I couldn't find an easy fix for now, it seems like merely adding add_output_handler to the ApacheMP2 request is enough to crash