[Seaside] Chaining problem

[an organic]

Hello
can anybody please explain me this example:

in init i make:
left := OrderedCollection new.
left add: nil -> 'Eukaryota'.
left add: 'Eukaryota' -> 'Opisthokonts'.

and then in another method:
(self perform: #left) do: [ :item | ...]


it's ok, but if i change init to
left := OrderedCollection new add: nil -> 'Eukaryota'; add: 'Eukaryota' ->
'Opisthokonts'.

and then i call
(self perform: #left) do: [ :item | ...]
i get error

i thought both init are equivalent

thnx.
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