Directory information for unixPath, or null if unixPath denotes a root directory or is null. Returns String.Empty if unixPath does not contain directory information.
unixPath contains Unix filesystem-illegal characters (NUL), is empty, or contains only white spaces.
Remarks
In most cases, the string returned by this method consists of all characters in the path up to but not including the last UnixDirectorySeparatorChar. If the path consists of a root ("/"), null is returned.