Validating InitialDirectory for SaveFileDialog?

I'm opening a SaveFileDialog with an initial directory based on a user-defined path. I want make sure this path is valid before passing it in and opening the dialog. Right now I've got this:

Microsoft.Win32.Sa开发者_运维知识库veFileDialog dialog = new Microsoft.Win32.SaveFileDialog();

if (!string.IsNullOrEmpty(initialDirectory) && Directory.Exists(initialDirectory))
{
    dialog.InitialDirectory = initialDirectory;
}

bool? result = dialog.ShowDialog();

However, it seems \ is slipping by and causing a crash when I call ShowDialog. Are there other values that could cause crashes? What rules does the InitialDirectory property need to follow?

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The quick and easy way to fix it would be to get the full path:

dialog.InitialDirectory = Path.GetFullPath(initialDirectory);

This will expand relative paths to the absolute ones that the SaveFileDialog expects. This will expand just about anything that resembles a path into a full, rooted path. This includes things like "/" (turns into the root of whatever drive the current folder is set to) and "" (turns into the current folder).