Image build failed

Build logs

Building in Docker Cloud’s infrastructure…
Cloning into ‘.’…
Warning: Permanently added the RSA host key for IP address ‘’ to the list of known hosts.
error: Your local changes to the following files would be overwritten by checkout:
Please, commit your changes or stash them before you can switch branches.
please ensure the correct public key is added to the list of trusted keys for this repository and the remote branch exists. (1)

I trigger the build through GitHub, why local changes exists? It should always reset hard to the commit version.