Added support for the CPNullPlaceholderBindingOption for bound text fields.

AppKit/CPKeyValueBinding.j

@@ -430,6 +430,7 @@ CPOptionsKey            = @"CPOptionsKey";
 CPMultipleValuesMarker  = @"CPMultipleValuesMarker";
 CPNoSelectionMarker     = @"CPNoSelectionMarker";
 CPNotApplicableMarker   = @"CPNotApplicableMarker";
+CPNullMarker            = @"CPNullMarker";
 
 // Binding name constants
 CPAlignmentBinding      = @"alignment";
@@ -470,5 +471,5 @@ CPValueTransformerBindingOption                     = @"CPValueTransformer";
 
 CPIsControllerMarker = function(/*id*/anObject)
 {
-    return anObject === CPMultipleValuesMarker || anObject === CPNoSelectionMarker || anObject === CPNotApplicableMarker;
+    return anObject === CPMultipleValuesMarker || anObject === CPNoSelectionMarker || anObject === CPNotApplicableMarker || anObject === CPNullMarker;
 }

AppKit/CPObjectController.j

@@ -663,7 +663,7 @@ var CPObjectControllerContentKey                        = @"CPObjectControllerCo
 
 - (id)_controllerMarkerForValues:(CPArray)theValues
 {
- var count = [theValues count];
+    var count = [theValues count];
 
     if (!count)
         value = CPNoSelectionMarker;
@@ -685,6 +685,9 @@ var CPObjectControllerContentKey                        = @"CPObjectControllerCo
         }
     }
 
+    if (value === nil || value.isa && [value isEqual:[CPNull null]])
+        value = CPNullMarker;
+
     return value;
 }
 

AppKit/CPTextField.j

@@ -1404,6 +1404,10 @@ var CPTextFieldIsEditableKey            = "CPTextFieldIsEditableKey",
 
                 newValue = [options objectForKey:CPNotApplicablePlaceholderBindingOption] || @"Not Applicable";
                 break;
+
+            case CPNullMarker:
+                newValue = [options objectForKey:CPNullPlaceholderBindingOption] || @"";
+                break;
         }
 
         [_source setPlaceholderString:newValue];