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aibump2d is meant to be used differently now. Before it had to be inserted at the root of the shading tree, and you connected the surface shader in this attribute "shader".
Now it's the other way around, you need to connect aibump2d to the surface shader's attribute "normal" (or "normalCamera"). That's why the parameter "shader" no longer exists.
New aibump2d now just work like maya bump2d node,connect to the "normal camera" of the shader
i was looking in the docs and this new way to use thre shader has not yet been updated!;)