fix findUndeclaredVariableIn:

src/Kernel/UndefinedObject.class.st

@@ -123,7 +123,7 @@ UndefinedObject >> findUndeclaredVariableIn: ast [
 	"Walk the ast of the current statment and find the undeclared variable node, or nil (if none).
 	Assumes there is only one such variable in an executing statement"
 
-	^ast nodes detect: [:node | node isVariable and: [ node isUndeclared]] ifNone: [ nil ]
+	^ast variableNodes detect: [:node | node isUndeclared] ifNone: [ nil ]
 ]
 
 { #category : #testing }