Composite Extract Method fails to extarct statement

[balsa-sarenac]

Pharo13 (didn't test on Pharo14 should be the same behavior)

It fails when parsing this statement: self addChild: OCVariableNode(aChild).

To reproduce, try this:

SoupTag >> beParentOf: anElement
	children ifNotEmpty: [anElement previousSibling: children last].
	children add: anElement.
	```

try to extract `children add: anElement`.