Git Modification Check Failed Error in Thoughtworks Go.CD

Question

I am getting the following error in Thoughtworks Go for one of the projects, what does it mean and how can I fix it?

Modification check failed for material: URL: https://username:******@bitbucket.org/company/project.git, Branch: [Mar-03 17:08:55] Error performing command: --- Command --- git rev-parse --abbrev-ref HEAD --- Environment --- {} --- INPUT ---- --OUTPUT --- HEAD --- ERROR --- STDERR: fatal: ambiguous argument 'HEAD': unknown revision or path not in the working tree. STDERR: Use '--' to separate paths from revisions, like this: STDERR: 'git [...] -- [...]' ---

Answer 1

If you look at the pipeline XML, there was one where the material had set the branch to be an empty string like so: branch="". Once I deleted this, the error went away.