Broken functionality with Pyramid 1.4

[zakdances]

After updating to Pyramid 1.4, pyramid_beaker no longer works with my app. My beaker factory has been configured with session.type = file, but nothing is being written to the data directory and no session cookies are ever set. It's just silently failing. Are you able to reproduce this?

[zakdances]

After some investigation, it looks like this failure occurs when trying to set non-string values such as binaries in the session (in other words, non-picklable values). Trying to store something like a UUID binary will result in beaker's session failing without any warnings or exceptions, despite what the documentation says.