dart:io | The empty path should return "." for its toNativePath value.

sdk/lib/io/path.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 /**
  * A Path is an immutable wrapper of a String, with additional member functions
  * for useful path manipulations and queries.
  * On the Windows platform, Path also converts from native paths to paths using
@@ skipping 110 matching lines @@
    *
    * To compute a relative path using URL semantics, where the final
    * path component of the base is dropped unless it ends with a slash,
    * call [: a.relativeTo(b.directoryPath) :] instead of [: a.relativeTo(b) :].
    */
   Path relativeTo(Path base);
 
   /**
    * Converts a path to a string using the native filesystem's conventions.
    *
+   * Always returns '.' if the path is empty.
    * On Windows, converts '/'s to backwards slashes, and removes
    * the leading '/' if the path starts with a drive specification.
    * For most valid Windows paths, this should be the inverse of the
    * conversion that the constructor new Path() performs.  If the path is
    * a Windows share, restores the '\\' at the start of the path.
    */
   String toNativePath();
 
   /**
    * Returns the path as a string.  If this path is constructed using
@@ skipping 57 matching lines @@
 
   /**
    * The part of [filename] after the last '.', or '' if [filename]
    * contains no '.'.  If [filename] is '.' or '..', returns ''.
    *
    *     new Path('tiger.svg').extension == 'svg'
    *     new Path('/src/dart/dart_secrets').extension == ''
    */
   String get extension;
 }