"mojo bundle-show" doesn't show the bundle

While trying to convert a spec to use bundles, I ran:

$ mojo bundle-show --options config=bundle.yaml local=deploy-secrets -p mojo-lp-signing -w devel -s bionic --stage mojo-lp-signing/devel --spec-url 'git+https://git.launchpad.net/~cjwatson/launchpad-mojo-specs;revno=signing-bundle,overwrite=true'
2020-04-17 17:40:05 [INFO] Using pre-existing container class containerless
2020-04-17 17:40:05 [INFO] Cloning repository at /home/cjwatson/.local/share/mojo/mojo-lp-signing/bionic/devel/spec from https://git.launchpad.net/~cjwatson/launchpad-mojo-specs
2020-04-17 17:40:08 [INFO] Repository /home/cjwatson/.local/share/mojo/mojo-lp-signing/bionic/devel/spec at ref signing-bundle revision 51f2c7848e338146dc56cb583e8449461eb30964
2020-04-17 17:40:08 [INFO] Updating submodules in repository /home/cjwatson/.local/share/mojo/mojo-lp-signing/bionic/devel/spec
2020-04-17 17:40:09 [INFO] Showing deployment configuration.

It doesn't actually show the bundle. This doesn't seem very useful - I see that DeployerPhase.show (which worked last time I tried it) uses print() while BundlePhase.show uses logging.getLogger('file').info(), so maybe that has something to do with it?