brew updateがNo such file or directoryで失敗したとき

$brew update
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
/usr/local/Library/brew.sh: line 32: /usr/local/Library/ENV/scm/git: No such file or directory
Error: update-report should not be called directly!

時折発生する事象らしい。
以下のコマンドで最新版にresetすると直る。

cd "$(brew --repository)" && git fetch && git reset --hard origin/master

ref. https://discuss.circleci.com/t/brew-update-command-fails/5211