node 8.9.1
shelljs 0.8.1
mac osx

I expect this code to not produce any output but it does.

const shell = require('shelljs');

shell.exec('git rev-parse --abbrev-ref  master2@{upstream}', {silent:true});

Run it in a git repository that does not have a branch master2 and you should see an error printed

exec: fatal: no such branch: 'master2'