New: Sort using descriptors handles nil and CPNull in correct way

This is the same way as Cocoa works.
Also added test case.

Foundation/CPArray/CPMutableArray.j

@@ -429,6 +429,9 @@ var sortArrayUsingFunction = function(array, aFunction, aContext)
     }
 }
 
+// This is for speed
+var CPMutableArrayNull = [CPNull null];
+
 // Observe that the sort descriptors has the reversed order by the caller
 var sortArrayUsingJSDescriptors = function(a, d)
 {
@@ -451,7 +454,10 @@ var sortArrayUsingJSDescriptors = function(a, d)
         aUID,
         bUID,
         key,
-        dd;
+        dd,
+        value1,
+        value2,
+        cpNull = CPMutableArrayNull;
 
     if (dl < 0)
         return;
@@ -519,7 +525,14 @@ var sortArrayUsingJSDescriptors = function(a, d)
                 {
                     dd = d[cn];
                     key = dd.k;
-                    o = objj_msgSend(C1[key], dd.s, C2[key]);
+                    value1 = C1[key];
+                    value2 = C2[key];
+                    if (value1 === nil || value1 === cpNull)
+                        o = value2 === nil || value2 === cpNull ? CPOrderedSame : CPOrderedAscending;
+                    else
+                    {
+                        o = value2 === nil || value2 === cpNull ? CPOrderedDescending : objj_msgSend(value1, dd.s, value2);
+                    }
 
                     if (o && !dd.a)
                         o = -o;

Tests/Foundation/CPMutableArrayTest.j

@@ -470,6 +470,26 @@
     [self assert:[5, 4, 4, 3, 2, 2, 1, 1, 1, 1] equals:target];
 }
 
+- (void)testThatCPArrayDoesSortCorrectWithNilAndCPNull
+{
+    var descriptors = [[CPSortDescriptor sortDescriptorWithKey:@"number" ascending:NO]],
+        target = [
+                    [[CPPrettyObject alloc] initWithValue:@"a" number:nil],
+                    [[CPPrettyObject alloc] initWithValue:@"a" number:[CPNull null]],
+                    [[CPPrettyObject alloc] initWithValue:@"a" number:@"Objective-J"],
+                    [[CPPrettyObject alloc] initWithValue:@"a" number:[CPNull null]],
+                    [[CPPrettyObject alloc] initWithValue:@"a" number:nil],
+                 ];
+
+    [target sortUsingDescriptors:descriptors];
+
+    [self assert:@"Objective-J" equals:[target[0] number]];
+    [self assert:nil equals:[target[1] number]];
+    [self assert:[CPNull null] equals:[target[2] number]];
+    [self assert:[CPNull null] equals:[target[3] number]];
+    [self assert:nil equals:[target[4] number]];
+}
+
 - (void)testMutableCopy
 {
     var normalArray = [],