[BPT] Not possible to build as empty user/channel.

[grafikrobot]

Description of Problem, Request, or Question

It appears it's not possible to build/create in CI as lib/x.y.z@ (aka lib/x.y.z@_/_. Setting CONAN_USER=_ and CONAN_CHANNEL=_ errors. As does setting them to CONAN_USER= and CONAN_CHANNEL=.

Package and Environment Details (include every applicable attribute)

• Conan version: Conan 1.36.0
• Python version: Python 3.9.4

[Croydon]

Do you have any logs? Whats happens if you try?

[grafikrobot]

Logs for when one sets CONAN_USERNAME="" and CONAN_PASSWORD="".. https://github.com/bfgroup/conan/runs/2495572707?check_suite_focus=true#step:5:52
You get something similar if you set them to both to "_" also.