Merge pull request #627 from Hitsu91/master

RxList null check in the constructor

@@ -11,7 +11,7 @@ import '../rx_typedefs/rx_typedefs.dart';
 /// Create a list similar to `List<T>`
 class RxList<E> implements List<E>, RxInterface<List<E>> {
   RxList([List<E> initial]) {
-    _list = initial;
+    if (initial != null) _list = initial;
   }
 
   List<E> _list = <E>[];

@@ -9,7 +9,7 @@ import '../rx_typedefs/rx_typedefs.dart';
 
 class RxMap<K, V> implements RxInterface<Map<K, V>>, Map<K, V> {
   RxMap([Map<K, V> initial]) {
-    _value = initial;
+    if (initial != null) _value = initial;
   }
 
   @override

@@ -9,7 +9,7 @@ import '../rx_typedefs/rx_typedefs.dart';
 
 class RxSet<E> implements Set<E>, RxInterface<Set<E>> {
   RxSet([Set<E> initial]) {
-    _set = initial;
+    if (initial != null) _set = initial;
   }
 
   Set<E> _set = <E>{};