fix little bug with notify on change

Group.cs

@@ -12,15 +12,15 @@ namespace YOUserbase {
 
         private static int index = 0;
 
-        public Group () {
+        public Group() {
             Id = ++index;
         }
 
         // Wrpper to change vaulue and notify if it changed
-        private void ChangeValue<T> (ref T field, T value, [CallerMemberName] string propertyName = "") {
+        private void ChangeValue<T>(ref T field, T value, [CallerMemberName] string propertyName = "") {
             if(!value.Equals(field)) {
                 field = value;
-                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
+                if(PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
             }
         }
 

User.cs

@@ -26,19 +26,19 @@ namespace YOUserbase {
 
         private static int index = 0;
 
-        public User () {
+        public User() {
             Id = ++index;
         }
 
-        public User (int id) {
+        public User(int id) {
             Id = id;
         }
 
         // Wrpper to change vaulue and notify if it changed
-        private void ChangeValue<T> (ref T field, T value, [CallerMemberName] string propertyName = "") {
+        private void ChangeValue<T>(ref T field, T value, [CallerMemberName] string propertyName = "") {
             if(!value.Equals(field)) {
                 field = value;
-                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
+                if(PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
             }
         }