Code crashes without any concrete error and no help documents

从 issue 中展示的基本示例开始，复现经过 Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args) 的启动路径。检查无 verb 时如何报告结果，以及显示的错误是否为此示例提供了足够的指导。当对于不带命令运行该示例的用户而言，启动行为和调试指导都清晰时，即视为完成。

Basic example crashes with this error on start:

ERROR(S):
No verb selected.
add Add file contents to the index.
commit Record changes to the repository.
clone Clone a repository into a new directory.
help Display more information on a specific command.
version Display version information.

Process finished with exit code 1.

• If I need to debug it, how it's being done?

 [Verb("add", HelpText = "Add file contents to the index.")]
    class AddOptions {
        //normal options here
    }
    [Verb("commit", HelpText = "Record changes to the repository.")]
    class CommitOptions {
        //commit options here
    }
    [Verb("clone", HelpText = "Clone a repository into a new directory.")]
    class CloneOptions {
        //clone options here
    }

    static int Main(string[] args) {
        return CommandLine.Parser.Default.ParseArguments<AddOptions, CommitOptions, CloneOptions>(args)
            .MapResult(
                (AddOptions opts) => RunAddAndReturnExitCode(opts),
                (CommitOptions opts) => RunCommitAndReturnExitCode(opts),
                (CloneOptions opts) => RunCloneAndReturnExitCode(opts),
                errs => 1);
    }

    private static int RunCloneAndReturnExitCode(CloneOptions opts)
    {
        return 1;
    }

    private static int RunCommitAndReturnExitCode(CommitOptions opts)
    {
        return 1;
    }

    private static int RunAddAndReturnExitCode(AddOptions opts)
    {
        return 0;
    }
}