The git command 'git status --short' is porcelain and may
incorrectly identify clean git trees as dirty if
status.branch git config is set.
Use git-diff-index plumbing instead.

The bug can be reproduced globally for all trees
or locally in just one by setting git config variable
"status.branch" to true. The command "git status --short"
will then print a header with branch tracking information

• i.e. always print something.

With such a git config, the stashAndUpdate always stashes.
The "git stash push" command for a clean tree succeeds by doing nothing.
Then "git stash pop" command fails because there is nothing to pop.