build isn't executed before checking for rootfs

[malachid]

If I specify 'files', the build step is executed to generate the required files and everything runs.
(see: https://github.com/malachid/capstan-gradle-example-java/tree/master)

If I specify 'rootfs' instead of 'files', the build step is not executed. It says it can not find the specified directory or Capstanfile, and fails to run.
(see https://github.com/malachid/capstan-gradle-example-java/tree/capstan_163)

If I execute the build step manually before running capstan, it runs fine.

I would expect the build to be run, to auto-generate the rootfs, to be included.