diff --git a/SOPE/NGCards/CardElement.h b/SOPE/NGCards/CardElement.h
index ebd89f1e4..de633d07c 100644
--- a/SOPE/NGCards/CardElement.h
+++ b/SOPE/NGCards/CardElement.h
@@ -33,7 +33,7 @@
 
 @class CardGroup;
 
-@interface CardElement : NSObject <NSCopying>
+@interface CardElement : NSObject <NSCopying, NSMutableCopying>
 {
   NSString *tag;
   NSMutableArray *values;
@@ -56,7 +56,7 @@
                values: (NSArray *) someValues;
 
 - (void) setParent: (CardGroup *) aParent;
-- (CardGroup *) parent;
+- (id) parent;
 
 - (void) setTag: (NSString *) aTag;
 
diff --git a/SOPE/NGCards/CardElement.m b/SOPE/NGCards/CardElement.m
index cc3697556..9767359b6 100644
--- a/SOPE/NGCards/CardElement.m
+++ b/SOPE/NGCards/CardElement.m
@@ -116,7 +116,7 @@
   parent = aParent;
 }
 
-- (CardGroup *) parent
+- (id) parent
 {
   return parent;
 }
@@ -524,4 +524,19 @@
   return new;
 }
 
+/* NSMutableCopying */
+- (id) mutableCopyWithZone: (NSZone *) aZone
+{
+  CardElement *new;
+
+  new = [[self class] new];
+  [new setTag: [tag mutableCopyWithZone: aZone]];
+  [new setGroup: [group mutableCopyWithZone: aZone]];
+  [new setParent: parent];
+  [new setValuesAsCopy: [values mutableCopyWithZone: aZone]];
+  [new setAttributesAsCopy: [attributes mutableCopyWithZone: aZone]];
+
+  return new;
+}
+
 @end
diff --git a/SOPE/NGCards/CardGroup.h b/SOPE/NGCards/CardGroup.h
index 6800f0769..1dfb6c7ef 100644
--- a/SOPE/NGCards/CardGroup.h
+++ b/SOPE/NGCards/CardGroup.h
@@ -29,7 +29,7 @@
 @class NSMutableArray;
 @class NSString;
 
-@interface CardGroup : CardElement <NSCopying>
+@interface CardGroup : CardElement <NSCopying, NSMutableCopying>
 {
   NSMutableArray *children;
 }
diff --git a/SOPE/NGCards/CardGroup.m b/SOPE/NGCards/CardGroup.m
index fc45e695e..330634964 100644
--- a/SOPE/NGCards/CardGroup.m
+++ b/SOPE/NGCards/CardGroup.m
@@ -159,29 +159,32 @@ static NGCardsSaxHandler *sax = nil;
   NSString *childTag;
   CardElement *newChild;
 
-  childTag = [aChild tag];
-  newChild = nil;
-  mappedClass = [self classForTag: [childTag uppercaseString]];
-  if (mappedClass)
+  if (aChild)
     {
-      if (![aChild isKindOfClass: mappedClass])
-        {
-          NSLog (@"warning: new child to entity '%@': '%@' converted to '%@'",
-                 tag, childTag, NSStringFromClass(mappedClass));
-          if ([aChild isKindOfClass: [CardGroup class]])
-            newChild = [(CardGroup *) aChild groupWithClass: mappedClass];
-          else
-            newChild = [aChild elementWithClass: mappedClass];
-        }
-    }
-//   else
-//     NSLog (@"warning: no mapped class for tag '%@'",
-//            childTag);
+      childTag = [aChild tag];
+      newChild = nil;
+      mappedClass = [self classForTag: [childTag uppercaseString]];
+      if (mappedClass)
+	{
+	  if (![aChild isKindOfClass: mappedClass])
+	    {
+	      NSLog (@"warning: new child to entity '%@': '%@' converted to '%@'",
+		     tag, childTag, NSStringFromClass(mappedClass));
+	      if ([aChild isKindOfClass: [CardGroup class]])
+		newChild = [(CardGroup *) aChild groupWithClass: mappedClass];
+	      else
+		newChild = [aChild elementWithClass: mappedClass];
+	    }
+	}
+      //   else
+      //     NSLog (@"warning: no mapped class for tag '%@'",
+      //            childTag);
 
-  if (!newChild)
-    newChild = aChild;
-  [children addObject: newChild];
-  [newChild setParent: self];
+      if (!newChild)
+	newChild = aChild;
+      [children addObject: newChild];
+      [newChild setParent: self];
+    }
 }
 
 - (CardElement *) uniqueChildWithTag: (NSString *) aTag
@@ -214,17 +217,20 @@ static NGCardsSaxHandler *sax = nil;
   NSString *childTag;
   NSEnumerator *existing;
 
-  childTag = [aChild tag];
-  existing = [[self childrenWithTag: childTag] objectEnumerator];
-
-  currentChild = [existing nextObject];
-  while (currentChild)
+  if (aChild)
     {
-      [children removeObject: currentChild];
-      currentChild = [existing nextObject];
-    }
+      childTag = [aChild tag];
+      existing = [[self childrenWithTag: childTag] objectEnumerator];
 
-  [self addChild: aChild];
+      currentChild = [existing nextObject];
+      while (currentChild)
+	{
+	  [children removeObject: currentChild];
+	  currentChild = [existing nextObject];
+	}
+
+      [self addChild: aChild];
+    }
 }
 
 - (CardElement *) firstChildWithTag: (NSString *) aTag;
@@ -260,12 +266,8 @@ static NGCardsSaxHandler *sax = nil;
   NSEnumerator *newChildren;
 
   newChildren = [someChildren objectEnumerator];
-  currentChild = [newChildren nextObject];
-  while (currentChild)
-    {
-      [self addChild: currentChild];
-      currentChild = [newChildren nextObject];
-    }
+  while ((currentChild = [newChildren nextObject]))
+    [self addChild: currentChild];
 }
 
 - (NSArray *) children
@@ -343,9 +345,14 @@ static NGCardsSaxHandler *sax = nil;
 
 - (void) setChildrenAsCopy: (NSMutableArray *) someChildren
 {
-  [children release];
-  children = someChildren;
-  [children retain];
+  NSEnumerator *list;
+  CardElement *currentChild;
+
+  ASSIGN (children, someChildren);
+
+  list = [children objectEnumerator];
+  while ((currentChild = [list nextObject]))
+    [currentChild setParent: self];
 }
 
 - (void) addChildWithTag: (NSString *) aTag
@@ -358,12 +365,8 @@ static NGCardsSaxHandler *sax = nil;
 
   newChild = [CardElement simpleElementWithTag: aTag value: aValue];
   types = [someTypes objectEnumerator];
-  type = [types nextObject];
-  while (type)
-    {
-      [newChild addType: type];
-      type = [types nextObject];
-    }
+  while ((type = [types nextObject]))
+    [newChild addType: type];
 
   [self addChild: newChild];
 }
@@ -400,6 +403,8 @@ static NGCardsSaxHandler *sax = nil;
     [children replaceObjectAtIndex: index withObject: newElement];
 }
 
+/* NSCopying */
+
 - (id) copyWithZone: (NSZone *) aZone
 {
   CardGroup *new;
@@ -410,4 +415,16 @@ static NGCardsSaxHandler *sax = nil;
   return new;
 }
 
+/* NSMutableCopying */
+
+- (id) mutableCopyWithZone: (NSZone *) aZone
+{
+  CardGroup *new;
+
+  new = [super mutableCopyWithZone: aZone];
+  [new setChildrenAsCopy: [children mutableCopyWithZone: aZone]];
+
+  return new;
+}
+
 @end
diff --git a/SOPE/NGCards/ChangeLog b/SOPE/NGCards/ChangeLog
index ec0c0c542..f7d868350 100644
--- a/SOPE/NGCards/ChangeLog
+++ b/SOPE/NGCards/ChangeLog
@@ -1,3 +1,16 @@
+2007-11-18  Wolfgang Sourdeau  <wsourdeau@inverse.ca>
+
+	* CardGroup.m ([CardGroup -addChild:aChild]): don't process nil
+	values for aChild.
+	([CardGroup -setUniqueChild:aChild]): same as above.
+	([CardGroup -setChildrenAsCopy:someChildren]): reparent the copied
+	children.
+	([CardGroup -mutableCopyWithZone:aZone]): implemented
+	NSMutableCopying protocol.
+
+	* CardElement.m ([CardElement -mutableCopyWithZone:aZone]):
+	implemented NSMutableCopying protocol.
+
 2007-11-12  Wolfgang Sourdeau  <wsourdeau@inverse.ca>
 
 	* iCalTimeZonePeriod.m ([iCalTimeZonePeriod