Fix Advanced Search error for blank search terms

Ravi Kumarrequested to merge
633013-blank-query-notes-filter into master

What does this MR do and why?

Fixes a crash in Advanced Search when the search term is blank or only whitespace.

In Elastic::Latest::ApplicationClassProxy#basic_query_hash, the blank-query branch now includes filter: [] in query.bool. This gives it the same shape as the non-blank branch.

Code that runs later appends to that array: Search::Elastic::Filters#add_filter and SnippetClassProxy#filter. Without the array, they raised NoMethodError (undefined method 'concat' for nil and undefined method '<<' for nil). One example is a project merge request search with scope=merge_requests and search=%20. The Sentry issue is GITLABCOM-FJD9.

The fix is in the query builder, not a nil guard in add_filter. A guard would hide the mismatch, and the builder is the part that is inconsistent.

Why this started failing
  • Merge request search at project and group level also searches comments. It reaches note search through related_ids_for_notes.
  • Before commit 4a7b0c10 ("Use optimized auth in note ES query", 2025-07-24), note search used project_ids_filter. That method did filter ||= [], which hid the missing array.
  • The commit moved note search to a path that assumes the array exists, so blank queries started to fail.
Test coverage

I added a spec in ee/spec/lib/elastic/latest/note_class_proxy_spec.rb, "when the query is blank", at project level. It fails with NoMethodError without the fix.

References

Screenshots or screen recordings

Request: GET /api/v4/projects/1/search?scope=merge_requests&state=opened&search=%20

Before After
fjd9_before fjd9_after

Before, the request returns 500 Internal Server Error. After, it returns the merge request JSON.

How to set up and validate locally

  1. Use a GDK with Advanced Search enabled. In Admin > Settings > Search, turn on "Search with Advanced Search" and finish indexing.
  2. Sign in.
  3. Open https://gdk.test:3443/api/v4/projects/<id>/search?scope=merge_requests&state=opened&search=%20 for a project that has open merge requests.
  4. On master, the response is a 500 error. On this branch, it is JSON results.

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