Add the content of the package.

lib/src/none.dart

Index: lib/src/none.dart
diff --git a/lib/src/none.dart b/lib/src/none.dart
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index 0000000000000000000000000000000000000000..35970b51fc2aee839b5ddcd048287b4d106f8375
--- /dev/null
+++ b/lib/src/none.dart
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+// Copyright (c) 2016, 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.
+
+import '../boolean_selector.dart';
+
+/// A selector that matches no inputs.
+class None implements BooleanSelector {
+  final variables = const [];
+
+  const None();
+
+  bool evaluate(semantics) => false;
+
+  BooleanSelector intersection(BooleanSelector other) => this;
+
+  BooleanSelector union(BooleanSelector other) => other;
+
+  void validate(bool isDefined(String variable)) {}
+
+  String toString() => "<none>";
+}