[rubenvdlinde]

What

The aggregation endpoints (/api/objects/aggregations/{register}/{schema}, .../grouped, named aggregations) accept the list endpoint's "empty" / "filled" filter syntax:

• assignee=IS NULL and assignee=IS NOT NULL;
• assignee[isnull]=true|false (true, "true", "1", "on", "yes" ask for empty; anything else for filled).

"Empty" means a missing or SQL NULL value, exactly as on the list endpoint. Both the native SQL path (field IS NULL / IS NOT NULL; isnull no longer makes it bail) and the PHP fallback apply it.

One reader, not a second parser

The meaning lives in lib/Support/NullFilter.php (nullCheck(), isNullOperatorAsksForNull(), the IS NULL / IS NOT NULL / isnull constants). The list search (MagicSearchHandler::isNullOperatorAsksForNull()), nested-path filters (NestedPathFilter) and the aggregation runner all read it, so the endpoint that lists a page and the one that counts its chips cannot disagree about what "empty" is.

Authorization

Unchanged: the native path keeps the reader's row predicate (rbacRowPredicateSql) and organisation scope in the same WHERE; the PHP fallback filters the rows it already hydrated under the same rules.

Why

nextcloud-vue's quickFiltersFrom and chip counts count through the grouped aggregation with the page filter. On dossiq's Queue (assignee: IS NULL) IS NULL was compared as literal text (empty groups) and [isnull]=true was refused ("Unsupported aggregation filter operator isnull"), so the chips drew nothing while the list showed rows.

Also in this PR

Dutch for the OpenRegister flow step names and descriptions on the palette (53 strings in l10n/nl.json and l10n/nl.js; "When someone runs it" is "Als iemand hem start"), written without em-dashes.

Verified locally

• NullFilterTest (3, new), AggregationRunnerMultiValueFilterTest (17, 3 new: PHP fallback in every spelling, native grouped IS NULL and [isnull]=false SQL and counts), all of tests/Unit/Service/Aggregation/ (276), FilterParamsTest, MagicSearchHandlerIsNullOperatorTest, MagicSearchHandlerTest, MagicSearchHandlerNestedPathFilterTest: all OK. The new tests fail on development.
• phpcs and phpmd on the changed files: no findings on changed lines.
• composer check:strict once: lint, migration-version, phpcs, phpmd, psalm ("No errors found"), phpstan ("No errors") green; test:all 26,311 tests, 15 errors, the same inherited AuditTrail* / DraftRemovalAuditRow DB tests that need the server's OC\DB\Schema\Table (red on development too).

AI-assisted: written with Claude Code.