NodeBB <> Lemmy federation issue (re: nullable image/icon)

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nutomic@lemmy.ml reported a federation issue with a NodeBB instance and we debugged it. It turns out Lemmy is unable to handle actors who have image or icon set to null.

Lemmy is taking steps to handle this (source, source), and NodeBB will update its actor logic to omit properties without an avatar or cover photo set.

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@julian @nutomic null values are bad in JSON-LD. We really have to avoid them. There are some bad references to `null` in the AP spec; they're likely to get removed sometime soon.

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evan@cosocial.ca I had no idea that was the case. That is very good to know and having it called out in some sort of best practices doc (an existing w3c explainer?) would be helpful :smile:

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@julian @evan aside from potentially causing null pointer exceptions when you try to dereference null, using null is equivalent to just leaving out the statement in the first place. there's no reason to use null. the only time you'd need null values is if your schema required a certain key to be present but allowed the value to be nullable, which is generally a bad idea compared to just making the key optional. tony hoare, the inventor of null, called it their "billion-dollar mistake".

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trwnh@mastodon.social said in NodeBB <> Lemmy federation issue (re: nullable image/icon):
> using null is equivalent to just leaving out the statement in the first place.

That’s not true, there are specific scenarios where having an explicit “no value” is significant vs “missing value”…

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@julian if you give me any specific examples of when you would want to use null, i can recommend better alternatives. generally, it's always possible that there is missing information.

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trwnh@mastodon.social found one.

NodeBB uses audience to denote which audience an object (or context) belongs to.

Posts and Topics in NodeBB can belong to no context at all. null would be the way to communicate this, since omission might mean one isn’t specified.

Likewise, a Move(Context) where a topic is moved out of a category but not into another. You probably shouldnt omit target there.

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@julian no, null is the same as nothing. what you want is more like [] (the empty set). in the case where you Move something without a target, you should be sending an Update instead.

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trwnh@mastodon.social oh, another one.

Glitch-soc apparently lets you hide follower counts, and federates a -1. That works but null would be a more explicit statement that the follower collection is hidden/not accessible.

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@julian leaving out the totalItems statement entirely would do the same thing. the problem is when you ignore the (lack of) information presented and synthesize your own.

you could also define a vocab term for "hidden" or "unavailable", although this isn't much better than leaving it out in the first place

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@julian @trwnh i there are specifically processing problems with JSON-LD when an `id` property is `null`. I agree, we need better guidance. I'm adding an issue for it.

github.com/w3c/activitystreams

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NodeBB v4.6.1 contains the fix so that if an avatar and cover photo are not set, they are not included in the ActivityPub actor data.

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@julian love to see the reports of cross project colab!

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