Use of null in JSON-LD

[gkellogg]

Proposal: unless otherwise specified, the use of null as a value MUST be treated as if the value was never specified; i.e., it has no effect.

Proposal: unless otherwise specified, the use of null as a key is treated as if the key/value was never specified, and values of that key MUST NOT be processed.

Such uses MUST be removed when compacting.

[gkellogg]

Note that null can't be used as a key in JSON.

[gkellogg]

Uses within @context:

"@context": {
  "@language": null,
  "term": null,
  "prefix:term": null,
  "term": {"@id": null},
  "http://foo/bar": null
}

[niklasl]

Of potential value (e.g. for "probing", representing "inverse relations" etc.):

"isReferencedBy": {"@id": null, "@container": "@set"},

.. this is now described in depth in #84.

[msporny]

There are two ways null can be used in JSON-LD... in the @context and in the body of the document. I think we found consensus last time by stating that if 'null' is used in the value position in the body of the document, then a processor must ignore the key-value pair. If null is used in the @context, it has a number of different effects:

Clear the active context: "@context": null and "@context:" [null, ...]
Clear a term/prefix declaration: "term": null,
Clear the datatype associated with a term: "term": {"@id": "http://example.org/term", "@type": null}
Clear the language associated with a term: "term": {"@id": "http://example.org/term", "@language": null}
Clear the container type associated with a term: "term": {"@id": "http://example.org/term", "@container": null}

Any other places that null could be used?

[lanthaler]

"@id": null: clear the whole term declaration. What if that it's in the body? (see also #84)

Perhaps we should also define what happens if something like { "@value": null, "@language": "de" } is in the document.. I assume we just discard the whole typed/language-tagged literal.

The same for lists? Or should "@list": null" result in an empty list? (this is probably related to #79)

[lanthaler]

RESOLVED: Unless otherwise specified, when 'null' is used in the @context, it removes any definition associated with the key.

RESOLVED: If @context is set to 'null', then the active context is cleared or set to the initial context (depending on the resolution to ISSUE #80)

RESOLVED: Unless otherwise specified, if null is associated with a key in the body of a JSON-LD document, then the JSON-LD processor MUST act as if the key-value pair was never declared. If @value or @list is set to null in expanded form, then the entire JSON object is ignored.

[gkellogg]

In updating the algorithms, because the value must act as if it's not there, it results in data being removed when expanded, rather than compacted.