Omit empty pagination links

[mschneider85]

Purpose

I wanted to validate my API against the schema provided by json-api. There were validation errors caused by pagination links having "Null" values instead of strings. To make it schema compliant, I made this small modification.

Changes

An empty pagination link is serialized as nil, those are getting omitted now. This change affects the JsonApi adapter.

Caveats

Maybe omitting or returning empty pagination links should rather be optional?

Related GitHub issues

PR #1668 addresses a similar issue for links.

Additional helpful information

There's an open issue on the json-api repo pointing out the contradiction for pagination links within the specs. json-api/json-api#887

[bf4]

I wanted to validate my API against the schema provided by json-api.

The schema isn't authoritative. You shouldn't rely on it too strongly. Are null values allowed by the specs? I believe we recently added this behavior for the opposite reason.

[mschneider85]

The spec says

Each member of a links object is a “link”. A link MUST be represented as either:
a string containing the link’s URL.
an object (“link object”) [...]

For the pagination links (subset of links) it is:

Keys MUST either be omitted or have a null value

So I'm not quite sure how it is meant to be. In doubt I tended to follow the provided schema.

[bf4]

did not know about this on hash. thanks!

[bf4]

I assume you're vendoring the schema, in which case I suggest you modify it and consider submitting a PR to json schema to allow a nil value.