GitRepository.Config.BuildSignature throws an exception if user.name contains whitespace

For some reason I haven't yet figured out, my user.name setting is ' ' (a single whitespace). When I try to call GitRepository.Config.BuildSignature, it throws an exception instead of returning null

Reproduction steps

• Set your user.name setting to whitespace

using(var repo = new GitRepository(workingDirectory))
{
    var signature = repo.Config.BuildSignature(DateTimeOffset.Now);
}

Expected behavior

Return null

Actual behavior

Throws System.ArgumentException: 'String cannot be empty Parameter name: name'

Version of LibGit2Sharp (release number or SHA1)

0.26.2

Operating system(s) tested; .NET runtime tested

Windows 10,

從 GitRepository.Config.BuildSignature 開始，使用只包含空白字元的 user.name 值重現此問題。驗證遇到僅包含空白字元的名稱時，該方法會返回 null，而不是擲出 System.ArgumentException。