"null is not an object" after doing checkout -b

[danmoseley]

starting with http://onlywei.github.io/explain-git-with-d3/#fetchrebase:

git fetch Fetched 3 commits on master. git rebase master git rebase my-branch Already up-to-date. git checkout master git checkout master git commit git rebase origin/master git checkout my-branch git commit git rebase master git checkout dccdc4d git rebase my-branch Cannot find commit: null git checkout -b new null is not an object (evaluating 'this.getCommit('HEAD').tags')