-[NSCFString isGroup]: unrecognized selector

[mikeabdullah]

We're receiving a few error reports like the following:

1 libobjc.A.dylib 0x96a235a9 objc_exception_throw + 56
2 CoreFoundation 0x90167a21 -[NSException raise] + 17
3 ExceptionHandling 0x938a74c5 -[NSExceptionHandler _handleException:mask:] + 1877
4 ExceptionHandling 0x938a6d52 NSExceptionHandlerExceptionRaiser + 228
5 libobjc.A.dylib 0x96a235a9 objc_exception_throw + 56
6 CoreFoundation 0x9016990b -[NSObject(NSObject) doesNotRecognizeSelector:] + 187
7 CoreFoundation 0x900c2c06 ___forwarding___ + 950
8 CoreFoundation 0x900c27d2 _CF_forwarding_prep_0 + 50
9 iMedia 0x004a7f38 -[IMBNodeViewController selectNode:] + 47
10 iMedia 0x004b62da -[IMBObjectViewController openSubNode:] + 87
11 AppKit 0x95c08a26 -[NSApplication sendAction:to:from:] + 112
12 Sandvox 0x00063640 -[KSApplication sendAction:to:from:] + 192
13 AppKit 0x95c088d9 -[NSMenuItem _corePerformAction] + 435
14 AppKit 0x95c085ca -[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] + 174
15 AppKit 0x95c084b6 -[NSMenu performActionForItemAtIndex:] + 65
16 AppKit 0x95c08469 -[NSMenu _internalPerformActionForItemAtIndex:] + 50
17 AppKit 0x95c083cf -[NSMenuItem _internalPerformActionThroughMenuIfPossible] + 97
18 AppKit 0x95c08313 -[NSCarbonMenuImpl _carbonCommandProcessEvent:handlerCallRef:] + 336
19 AppKit 0x95bfca55 NSSLMMenuEventHandler + 404
20 HIToolbox 0x918c2c2f _ZL23DispatchEventToHandlersP14EventTargetRecP14OpaqueEventRefP14HandlerCallRec + 1567
21 HIToolbox 0x918c1ef6 _ZL30SendEventToEventTargetInternalP14OpaqueEventRefP20OpaqueEventTargetRefP14HandlerCallRec + 411
22 HIToolbox 0x918e47f3 SendEventToEventTarget + 52
23 HIToolbox 0x91910e87 _ZL18SendHICommandEventmPK9HICommandmmhPKvP20OpaqueEventTargetRefS5_PP14OpaqueEventRef + 448
24 HIToolbox 0x91935b90 SendMenuCommandWithContextAndModifiers + 66
25 HIToolbox 0x91935b47 SendMenuItemSelectedEvent + 121
26 HIToolbox 0x91935a5d _ZL19FinishMenuSelectionP13SelectionDataP10MenuResultS2_ + 152
27 HIToolbox 0x91ab7364 _ZL19PopUpMenuSelectCoreP8MenuData5PointdS1_tjPK4RecttmS4_S4_PK10__CFStringPP13OpaqueMenuRefPt + 1857
28 HIToolbox 0x91ab76bb _HandlePopUpMenuSelection7 + 678
29 AppKit 0x95e946e6 _NSSLMPopUpCarbonMenu3 + 3937
30 AppKit 0x95e94a76 -[NSCarbonMenuImpl _popUpContextMenu:withEvent:forView:withFont:] + 220
31 AppKit 0x9600d945 -[NSMenu _popUpContextMenu:withEvent:forView:withFont:] + 270
32 AppKit 0x9600d9e4 -[NSMenu _popUpContextMenu:withEvent:forView:] + 63
33 iMedia 0x004b7937 -[IMBObjectViewController imageBrowser:cellWasRightClickedAtIndex:withEvent:] + 127
34 ImageKit 0x9a4209fb -[IKImageBrowserView(ImageBrowserEvents) rightMouseDown:] + 376

Here's the bit I can't fathom:

As I understand it, the user right-clicked an object in the image browser and asked to Open it. For the Open menu to appear, the object has to be a folder. In all my tests, when doing that, this snippet of code from -openSubNode::

[inSender representedObject]

Always returns nil, so the feature doesn't work. Why is this feature broken? How does anybody ever get it to return anything other than nil?