CPNull is equal to CPNull. Unit test included.

Foundation/CPNull.j

@@ -44,6 +44,7 @@ var CPNullSharedNull = nil;
 
     return [super alloc];
 }*/
+
 /*!
     Returns the singleton instance of the CPNull
     object. While CPNull and \c nil should
@@ -57,6 +58,14 @@ var CPNullSharedNull = nil;
     return CPNullSharedNull;
 }
 
+- (BOOL)isEqual:(id)anObject
+{
+    if (self === anObject)
+        return YES;
+
+    return [anObject isKindOfClass:[CPNull class]];
+}
+
 /*!
     Returns CPNull null.
     @param aCoder the coder from which to do nothing

Tests/Foundation/CPNullTest.j

@@ -4,6 +4,12 @@
 
 @implementation CPNullTest : OJTestCase
 
+- (void)testEquals
+{
+    [self assert:[CPNull null] equals:[CPNull null] message:"CPNull null should equal itself."];
+    [self assert:[CPNull null] equals:[CPNull new] message:"CPNull null should equal another CPNull."];
+}
+
 - (void)testArchiving
 {
     [self assert:[CPKeyedUnarchiver unarchiveObjectWithData:[CPKeyedArchiver archivedDataWithRootObject:[CPNull null]]] equals:[CPNull null]];