The `nullable` keyword

Property definitions

	# The `nullable` keyword
	var n_kwnullable: TKwnullable is writable, noinit

src/parser/parser_nodes.nit:1568,2--1569,50

	redef fun n_kwnullable=(node)
	do
		_n_kwnullable = node
		node.parent = self
	end

src/parser/parser_prod.nit:8394,2--8398,4