The presence and depth of the debate about this formatting choice suggests that it isn't arbitrary. Many have provided solid reasons for why one option should be preferred over the other. They aren't merely articulating their opinions; they are also providing objective reasons for why their opinion is valid.

Everything about formatting is arbitrary, as long as it's consistent in a given codebase to the point of predictability (e.g. 90% consistent, not necessarily 100% consistent).

To elaborate a bit, sure, there are arguments for everything talked about here, and they're valid, but the marginal utility of any one choice is dwarfed by opting out of the arguments entirely, and just going with whatever Black has selected as a default.