You dont need check for array because you're creating it yourself... I'd write it like this:
```
gitHistory: function (branch, skipCommits) {
            var separator = "_._",
                items  = ["hashShort", "hash", "author", "date", "message"],
                format = ["%h",        "%H",   "%an",    "%ai",  "%s"     ].join(separator);
            
            var cmd = [
                this._git,
                "log",
                "-100",
                skipCommits ? "--skip=" + skipCommits : "",
                "--format=" + escapeShellArg(format),
                escapeShellArg(branch)
            ];
```

Please take note that you should write options like ```--skip``` before other things, you can find it in the documentation: https://www.kernel.org/pub/software/scm/git/docs/git-log.html

Reason is, invalid order might work on your Git implementation, but doesn't have to work on another one.