diff --git a/AppKit/CPMenu/CPMenu.j b/AppKit/CPMenu/CPMenu.j
index 8c00006d9..26ae6da2b 100644
--- a/AppKit/CPMenu/CPMenu.j
+++ b/AppKit/CPMenu/CPMenu.j
@@ -148,6 +148,13 @@ var _CPMenuBarVisible               = NO,
     return _CPMenuBarImage;
 }
 
++ (void)_setOrRemoveMenuBarAttribute:(id)aValue forKey:(id)aKey
+{
+    if (aValue === nil)
+        [_CPMenuBarAttributes removeObjectForKey:aKey];
+    else
+        [_CPMenuBarAttributes setObject:aValue forKey:aKey];
+}
 
 + (void)setMenuBarAttributes:(CPDictionary)attributes
 {
@@ -172,8 +179,8 @@ var _CPMenuBarVisible               = NO,
 
     else if (!textColor && !titleColor)
     {
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-text-color" forClass:_CPMenuView] forKey:@"CPMenuBarTextColor"];
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-title-color" forClass:_CPMenuView] forKey:@"CPMenuBarTitleColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-text-color" forClass:_CPMenuView] forKey:@"CPMenuBarTextColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-title-color" forClass:_CPMenuView] forKey:@"CPMenuBarTitleColor"];
     }
 
     if (!textShadowColor && titleShadowColor)
@@ -184,18 +191,18 @@ var _CPMenuBarVisible               = NO,
 
     else if (!textShadowColor && !titleShadowColor)
     {
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-text-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarTextShadowColor"];
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-title-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarTitleShadowColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-text-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarTextShadowColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-title-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarTitleShadowColor"];
     }
 
     if (!highlightColor)
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightColor"];
 
     if (!highlightTextColor)
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-text-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightTextColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-text-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightTextColor"];
 
     if (!highlightTextShadowColor)
-        [_CPMenuBarAttributes setObject:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-text-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightTextShadowColor"];
+        [self _setOrRemoveMenuBarAttribute:[[CPTheme defaultTheme] valueForAttributeWithName:@"menu-bar-highlight-text-shadow-color" forClass:_CPMenuView] forKey:@"CPMenuBarHighlightTextShadowColor"];
 
     if (_CPMenuBarSharedWindow)
     {
diff --git a/AppKit/CPSplitView.j b/AppKit/CPSplitView.j
index 3aedfa2e7..53b90ee1d 100644
--- a/AppKit/CPSplitView.j
+++ b/AppKit/CPSplitView.j
@@ -1156,8 +1156,14 @@ The sum of the views and the sum of the dividers should be equal to the size of
     {
         _preCollapsePositions = [CPMutableDictionary new];
 
-        for (var i = 0, count = [preCollapseArray count]; i < count; i++)
-            [_preCollapsePositions setObject:preCollapseArray[i] forKey:i + ""];
+        for (var i = 0, count = [preCollapseArray count]; i < count; i++) {
+            var item = preCollapseArray[i];
+
+            if (item === nil)
+                [_preCollapsePositions removeObjectForKey:i + ""];
+            else
+                [_preCollapsePositions setObject:item forKey:i + ""];
+        }
     }
 }
 
diff --git a/Foundation/CPDictionary.j b/Foundation/CPDictionary.j
index dc0dc5307..64bd54560 100755
--- a/Foundation/CPDictionary.j
+++ b/Foundation/CPDictionary.j
@@ -27,6 +27,9 @@
 @import "CPObject.j"
 #import "Ref.h"
 
+//FIXME: After release of 0.9.7 remove below variable
+var deprecatedMessage = YES;
+
 /* @ignore */
 @implementation _CPDictionaryValueEnumerator : CPEnumerator
 {
@@ -260,8 +263,19 @@
     {
         var i = [keyArray count];
 
-        while (i--)
-            [self setObject:objects[i] forKey:keyArray[i]];
+        while (i--) {
+            var aValue = objects[i],
+                aKey = keyArray[i];
+
+            if (aValue === nil || aKey === nil) {
+                deprecatedMessage = NO;
+                CPLog.warn(@"[" + [self className] + @" " + _cmd +  @"DEPRECATED: Attempt to insert nil object from objects[" + i + @"]");
+                objj_backtrace_print(CPLog.warn);
+                //FIXME: After release of 0.9.7 remove variable deprecatedMessage and change above line to this:
+                //[CPException raise:CPInvalidArgumentException reason:@"Attempt to insert nil object from objects[" + i + @"]"];
+            }
+            [self setObject:aValue forKey:aKey];
+        }
     }
 
     return self;
@@ -297,12 +311,18 @@
 
         for (; index < argCount; index += 2)
         {
-            var value = arguments[index];
+            var value = arguments[index],
+                aKey = arguments[index + 1];
 
-            if (value === nil)
-                continue;
+            if (value === nil || aKey === nil) {
+                deprecatedMessage = NO;
+                CPLog.warn(@"[" + [self className] + @" " + _cmd +  @"DEPRECATED: Attempt to insert nil object from objects[" + (index / 2 - 1) + @"]");
+                objj_backtrace_print(CPLog.warn);
+                //FIXME: After release of 0.9.7 remove variable deprecatedMessage and change above line to this:
+                //[CPException raise:CPInvalidArgumentException reason:@"Attempt to insert nil object from objects[" + (index / 2 - 1) + @"]"];
+            }
 
-            [self setObject:value forKey:arguments[index + 1]];
+            [self setObject:value forKey:aKey];
         }
     }
 
@@ -611,6 +631,22 @@
 */
 - (void)setObject:(id)anObject forKey:(id)aKey
 {
+    if (deprecatedMessage && aKey === nil) {
+        CPLog.warn(@"[" + [self className] + @" " + _cmd +  @"] DEPRECATED: Key cannot be nil");
+        objj_backtrace_print(CPLog.warn);
+        //FIXME: After release of 0.9.7 change above line to this:
+        //[CPException raise:CPInvalidArgumentException reason:@"Key cannot be nil"];
+    }
+
+    if (deprecatedMessage && anObject === nil) {
+        CPLog.warn(@"[" + [self className] + @" " + _cmd +  @"] DEPRECATED: Object cannot be nil (key: " + aKey + @")");
+        objj_backtrace_print(CPLog.warn);
+        //FIXME: After release of 0.9.7 change above line to this:
+        //[CPException raise:CPInvalidArgumentException reason:@"Object cannot be nil (key: " + aKey + @")"];
+    }
+
+    //FIXME: After release of 0.9.7 remove below line.
+    deprecatedMessage = YES;
     self.setValueForKey(aKey, anObject);
 }
 
diff --git a/Foundation/CPKeyedArchiver.j b/Foundation/CPKeyedArchiver.j
index 80f7a6689..e4e0d7bbd 100644
--- a/Foundation/CPKeyedArchiver.j
+++ b/Foundation/CPKeyedArchiver.j
@@ -503,7 +503,8 @@ var _CPKeyedArchiverEncodeObject = function(self, anObject, isConditional)
             }
         }
 
-        [self._replacementObjects setObject:object forKey:GUID];
+        if (object != nil && GUID != nil)
+            [self._replacementObjects setObject:object forKey:GUID];
     }
 
     // If we still don't have an object by this point, then return a
diff --git a/Foundation/CPUserDefaults.j b/Foundation/CPUserDefaults.j
index 967ae83a7..205330d35 100644
--- a/Foundation/CPUserDefaults.j
+++ b/Foundation/CPUserDefaults.j
@@ -342,7 +342,10 @@ var StandardUserDefaults;
     var data = [[self persistentStoreForDomain:aDomain] data],
         domain = data ? [CPKeyedUnarchiver unarchiveObjectWithData:data] : nil;
 
-    [_domains setObject:domain forKey:aDomain];
+    if (domain === nil)
+        [_domains removeObjectForKey:aDomain];
+    else
+        [_domains setObject:domain forKey:aDomain];
 
     _searchListNeedsReload = YES;
 }