The sign self is optional and it may be absent from the relative construction without affecting the grammaticality of the structure.
re, sq
self mushroom collect++ basket cl(6) / cl(?): ‘put in the basket’.
‘I’ll put in the basket the mushrooms that I find.’
(© Marta Mosella 2012. Reprinted with permission from Mosella, 2012: 176)
However, when the sign is not explicit it may trigger ambiguity between a relative construction reading and a counterfactual conditional reading.
re, sq
mushroom collect++ basket cl(6) / cl(?): ‘put in the basket’.
‘I’ll put in the basket the mushrooms that I find. / If I had found mushrooms I’d had put them in the basket.’
(© Marta Mosella 2012. Reprinted with permission from Mosella, 2012: 177)