I'm reading a page in a grammar book about the usage of なら. It says that S1ならS2 cannot be used if the completion or actualization of S1 brings about S2. For example:
春子のアパートへ行くなら一郎がいた。
I kind of understand how S2 depends on S1 happening, but it's not very intuitive.
Would this sentence be correct? Or incorrect because of the previously mentioned rule?
今度の土曜日は働かなくてはいけないなら悲しい