def Just(self):<EOL>
return self._compose_optic(optics.JustPrism())<EOL>
A prism that focuses the value inside a `lenses.maybe.Just`
        object.

            >>> from lenses import lens
            >>> from lenses.maybe import Just, Nothing
            >>> lens.Just()
            UnboundLens(JustPrism())
            >>> lens.Just().collect()(Just(1))
            [1]
            >>> lens.Just().collect()(Nothing())
            []
            >>> lens.Just().set(2)(Just(1))
            Just(2)
            >>> lens.Just().set(2)(Nothing())
            Nothing()