repo.getHeadBlob() returns null

[stewartlord]

From the context of an Atom package:

var editor = atom.workspace.getActiveEditor();
var dir = new Directory(editor.getPath());
atom.project.repositoryForDirectory(dir).then(
 (repo) => {
 var path = editor.getPath();
 var repo = repo.getRepo();
 var blob = repo.getHeadBlob(path);
 console.log(blob);
 }
);

The above produces null, but other methods, such as getHead() work fine.

[stewartlord]

Chatted with @kevinsawicki and this method works if you give it a path that is relative to the repository root!