Adding isNotEmpty property to collection and string.

pkg/mdv_observe/lib/src/observable_map.dart

 // Copyright (c) 2013, 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 mdv_observe;
 
 // TODO(jmesserly): this needs to be faster. We currently require multiple
 // lookups per key to get the old value.
 // TODO(jmesserly): this doesn't implement the precise interfaces like
 // LinkedHashMap, SplayTreeMap or HashMap. However it can use them for the
@@ skipping 74 matching lines @@
   }
 
   Iterable<K> get keys => _map.keys;
 
   Iterable<V> get values => _map.values;
 
   int get length =>_map.length;
 
   bool get isEmpty => length == 0;
 
+  bool get isNotEmpty => !isEmpty;
+
   bool containsValue(V value) => _map.containsValue(value);
 
   bool containsKey(K key) => _map.containsKey(key);
 
   V operator [](K key) => _map[key];
 
   void operator []=(K key, V value) {
     int len = _map.length;
     V oldValue = _map[key];
     _map[key] = value;
@@ skipping 35 matching lines @@
       });
       notifyPropertyChange(_LENGTH, len, 0);
     }
     _map.clear();
   }
 
   void forEach(void f(K key, V value)) => _map.forEach(f);
 
   String toString() => Maps.mapToString(this);
 }