Document that the `get_terms` filter can have null for `$taxonomies`

[dd32]

The get_terms filter currently documents that the filter passes an array as both the first and second parameters, which is normally true, except that the second can be null when not specified.

The simplest way to trigger this scenario is to query for get_terms( [ 'term_taxonomy_id' => ?? ] ); which has no taxonomies to pass.

This can cause PHP Warnings and PHP Fatal errors in code that doesn't expect it.

See some real world examples:

• ​https://github.com/WordPress/learn/pull/243
• ​https://github.com/Automattic/sensei/pull/4329

Trac ticket: https://core.trac.wordpress.org/ticket/54222

[audrasjb]

Moving this for 5.9 consideration.
I'm wondering whether this should also be documented in other functions (like wp_terms_checklist and many others) or not.
Otherwise the PR looks good to me.

[dd32]

Replying to audrasjb:

I'm wondering whether this should also be documented in other functions (like wp_terms_checklist and many others) or not.

I'm not sure where that comes into play having taken a quick look at those, this is just that one of the additional context parameters on the get_terms filter is documented wrong, doesn't affect the return value (which is already Documented as being literally almost anything WP_Term[]|int[]|string[]|string|WP_Error :) ).

[audrasjb]

Ok, makes sense to me, thanks for checking :)

[mukesh27]

PR looks good to me.

Ready to commit

[davidbaumwald]

In 52131:

Taxonomy: Document that the get_terms filter can have null for $taxonomies.

The get_terms filter currently documents that the filter passes an array as both the first and second parameters, which is normally true, except that the second can be null when not specified. This change updates the filter's docblock to indicate that the second parameter can also be of a null type.

Props dd32, audrasjb, mukesh27.
Fixes #54222.

Committed to core in changeset https://core.trac.wordpress.org/changeset/52131.