Open custom file, args is always empty

I have C# WinForm .NET 4.5 application. I set Project -> Properties -> Publish -> Options -> File Associations. This part seems to work because it sets icon that I selected and if I double click file with custom extension (in this case *.psi) it opens my application. But I am having hard time getting file name that was double clicked. Somehow my static void Main(string[] args) args are always empty.

Can anyone help me with what I am missing to open custom file with my application.

static void Main(string[] args)
    {
        if(args.Length > 0)
        {
            MessageBox.Show(args[0]);
        }else {
          MessageBox.Show("args is empty!");
        }

        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        DevExpress.Skins.SkinManager.EnableFormSkins();

        UserLookAndFeel.Default.SetSkinStyle(Properties.Settings.Default.ActiveSkinName);


        Application.Run(new MainForm(args));
    }