[Bug]: "Error: unknown (2): failed to solve: no build directives" on environment-only container-file build (0.5.0)

[srcshelton]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

The container-file at https://github.com/srcshelton/docker-gentoo-build/blob/master/gentoo-base/Dockerfile.env exists solely of ENV declarations to be inherited by downstream container-images. Attempting to container build it results in:

$ /usr/local/bin/container build --file Dockerfile.env --tag localhost/gentoo-env:latest . 
Error: unknown (2): failed to solve: no build directives

It should be possible to produce an image from a Container-file which consists only of ENV (and ARG) keywords.

Current behavior

Container-files which only perform environment-setup cannot be built.

Expected behavior

Container-files which only perform environment-setup are valid and so should produce a container-image when built.

Environment

- OS: macOS 26.0.1
- Xcode: Version 26.0.1 (17A400)
- Container: container CLI version 0.5.0 (build: release, commit: 48230f3)

Relevant log output

N/A

Code of Conduct

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