---The Whisker 0.92 CS contains this:
!Preferences class methodsFor: 'add preferences' stamp: 'dew 4/27/2000 16:35'!
addNonExistingPreference: prefSymbol category: categorySymbol default: defaultFlag balloonHelp: helpString
	"Add/initialize a preference if it does not already exist."

	(self allPreferenceFlagKeys includes: prefSymbol) ifTrue: [^ self].
[...]

---in combination with this:
MessageNotUnderstood: includes:

VM: Win32 - Squeak3.1alpha of 28 February 2001 [latest update: #3844]
Image: Squeak3.1alpha [latest update: #'Squeak3.1alpha' of 7 March 2001 update 3960]

False(Object)>>doesNotUnderstand:
Preferences class>>addNonExistingPreference:category:default:balloonHelp:
WhiskerBrowser class>>initializePreferences
[...]

---it seems "Preferences allPreferenceFlagKeys" returns "false".

I tried it in a Workspace, and that's the case; so I tried to look up the method, but it wasn't there !! Huh?
Slowly it came to my mind that Preferences might answer all queries of the form "Preferences nonexistentSelector" (nonexistent preferences) with "false", and that's the case, too.

So I looked into the recent updates, and sure enough, #3932 removes this method.
As this seems to be part of a bigger overhaul of the Preferences, I'm not sure where this functionality resides now.

"(Preferences allPreferenceObjects collect: [ :p | p name]) sort" seems to come close to the old method's behaviour.

Joern