Review url being optional for SplashRequest

[Gallaecio]

As part of #269, the url parameter to SplashRequest is no longer optional.

@elacuesta noticed that this is a backward-incompatible change. Moreover, the upcoming Scrapy 2.4 will make this change unnecessary (scrapy/scrapy#4835).

We should consider reverting that part of #269.

[lopuhin]

sounds good to me, thanks for the heads up @Gallaecio

[Rafiot]

Reverting 4154782 will do just that, so just go for it.

[protokoul]

Hi. Is this issue still relevant to the latest version of scrapy-splash? I reverted the changes in 4154782, ran the tests locally and no failures were noticed.

[Gallaecio]

Well, I think reverting that commit is precisely the goal. I assume you reverted the entire commit, nor just the non-test code, and that keeping the current test code and applying the rest of the commit would result in broken tests.

[protokoul]

Yes, I reverted the entire commit including the changes to the tests.

[Gallaecio]

My understanding is that, reverting the commit, scrapy-splash would fail with scrapy>=2,<2.4 if the URL is omitted, because the default URL uses the unsupported about: protocol.

The easiest solution I think would be to revert that commit and require scrapy>=2.4.